Honeycomb structure

ABSTRACT

There is disclosed a honeycomb structure including a honeycomb structure section, and a pair of band-like electrode sections arranged on a side surface of the honeycomb structure section, an electrical resistivity of the honeycomb structure section is from 1 to 200 Ωcm, in a cross section which is perpendicular to an extending direction of cells, the one electrode section is disposed on an opposite side of the other electrode section via the center O, an angle which is 0.5 time as large as a central angle of the electrode section is from 15 to 65°, and each of the electrode sections is formed so as to become thinner from a center portion in a peripheral direction toward both ends in the peripheral direction in the cross section which is perpendicular to the cell extending direction in a honeycomb structure.

TECHNICAL FIELD

The present invention relates to a honeycomb structure, and moreparticularly, it relates to a honeycomb structure which is a catalystcarrier, also functions as a heater by applying a voltage, and cansuppress a bias of a temperature distribution when applying the voltage.

BACKGROUND ART

Heretofore, a honeycomb structure made of cordierite and including aloaded catalyst has been used in the treatment of harmful substances inan exhaust gas discharged from a car engine. Moreover, it is also knownthat a honeycomb structure formed by using a sintered silicon carbidebody is used in the purification of the exhaust gas (e.g., see PatentDocument 1).

When the exhaust gas is treated by the catalyst loaded onto thehoneycomb structure, it is necessary to raise a temperature of thecatalyst to a predetermined temperature. However, at the start of theengine, the catalyst temperature is low, and hence there has been theproblem that the exhaust gas is not sufficiently purified.

In consequence, there has been investigated a method of disposing aheater made of a metal on an upstream side of a honeycomb structure ontowhich a catalyst is loaded, to raise a temperature of an exhaust gas(e.g., see Patent Document 2).

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-4136319-B-   Patent Document 2: JP-2931362-B

SUMMARY OF THE INVENTION

When the above heater is mounted on a car and used, a power source foruse in an electric system of the car is used in common, and the powersource having a high voltage of, for example, 200 V is used. However,the heater made of a metal has a low electric resistance, and hence whensuch a power source having the high voltage is used, there is theproblem that a current excessively flows, and impairs a power sourcecircuit sometimes.

Moreover, when the heater is made of the metal, a catalyst is not easilyloaded, even if the heater is processed into a honeycomb structure.Therefore, it has been difficult to integrate the heater and thecatalyst.

The present invention has been developed in view of the above-mentionedproblems, and an object thereof is to provide a honeycomb structurewhich is a catalyst carrier, also functions as a heater by applying avoltage, and can suppress a bias of a temperature distribution whenapplying the voltage.

To achieve the above-mentioned object, the present invention providesthe following honeycomb structure.

[1] A honeycomb structure comprising: a tubular honeycomb structuresection including porous partition walls which partition and form aplurality of cells extending from one end surface to the other endsurface to become through channels of a fluid, and an outer peripheralwall positioned in an outermost periphery; and a pair of electrodesections arranged on a side surface of the honeycomb structure section,wherein an electrical resistivity of the honeycomb structure section isfrom 1 to 200 Ωcm, each of the pair of electrode sections is formed intoa band-like shape extending in a cell extending direction of thehoneycomb structure section, the one electrode section in the pair ofelectrode sections is disposed on an opposite side of the otherelectrode section in the pair of electrode sections via the center ofthe honeycomb structure section in a cross section which isperpendicular to the cell extending direction, an angle which is 0.5time as large as a central angle of each of the electrode sections isfrom 15 to 65° in the cross section which is perpendicular to the cellextending direction, and each of the electrode sections is formed so asto become thinner from a center portion in a peripheral direction towardboth ends in the peripheral direction in the cross section which isperpendicular to the cell extending direction.

[2] The honeycomb structure according to [1], wherein each of theelectrode sections is constituted of the center portion in theperipheral direction, and expanded portions positioned on both sides ofthe center portion in the peripheral direction in the cross sectionwhich is perpendicular to the cell extending direction, and theelectrical resistivity of the center portion of the electrode section issmaller than that of each of the expanded portions of the electrodesection.

[3] The honeycomb structure according to [2], wherein the electricalresistivity of the center portion of the electrode section is from 0.1to 10 Ωcm.

[4] The honeycomb structure according to [2] or [3], wherein theelectrical resistivity of the expanded portion of the electrode sectionis from 0.1 to 100 Ωcm.

[5] The honeycomb structure according to any one of [2] to [4], whereina thickness of the center portion of the electrode section is from 0.2to 5.0 mm.

[6] The honeycomb structure according to any one of [2] to [5], whereinin the cross section which is perpendicular to the cell extendingdirection, the angle which is 0.5 time as large as the central angle ofthe center portion of the electrode section is from 5 to 250.

[7] The honeycomb structure according to [1], wherein each of theelectrode sections does not have any boundary portion and iscontinuously formed in the cross section which is perpendicular to thecell extending direction.

[8] The honeycomb structure according to [7], wherein the electricalresistivity of the electrode sections is from 0.1 to 100 Ωcm.

[9] The honeycomb structure according to any one of [1] to [8], whereinat a center position of the center portion of each of the electrodesections in the cell extending direction, there is disposed an electrodeterminal protruding portion to which an electric wiring is fastened.

EFFECT OF THE INVENTION

In the honeycomb structure of the present invention, the electricalresistivity of the honeycomb structure section is from 1 to 200 Ωcm, andhence even when a current is allowed to flow by using a power sourcehaving a high voltage, the current does not excessively flow, whereby itis possible to suitably use the honeycomb structure as a heater.Moreover, “each of the pair of electrode sections is formed into theband-like shape extending in the cell extending direction of thehoneycomb structure section, the one electrode section in the pair ofelectrode sections is disposed on the opposite side of the otherelectrode section in the pair of electrode sections via the center ofthe honeycomb structure section in the cross section which isperpendicular to the cell extending direction, the angle which is 0.5time as large as the central angle of each of the electrode sections isfrom 15 to 65° in the cross section which is perpendicular to the cellextending direction”, and hence it is possible to suppress a bias of atemperature distribution when applying the voltage.

Furthermore, “each of the electrode sections is formed so as to becomethinner from the center portion in the peripheral direction toward boththe ends in the peripheral direction in the cross section which isperpendicular to the cell extending direction”, and hence it is possibleto further suppress the bias of the temperature distribution whenapplying the voltage.

In addition, “each of the electrode sections is constituted of thecenter portion in the peripheral direction, and expanded portionspositioned on both sides of the center portion in the peripheraldirection in the cross section which is perpendicular to the cellextending direction, the electrical resistivity of the center portion ofthe electrode section is smaller than that of each of the expandedportions of the electrode section, and each of the expanded portions isformed so as to become thinner from an end portion which comes incontact with the center portion toward a side edge which is the oppositeend portion in the cross section which is perpendicular to the cellextending direction.” Also in this case, it is possible to furthersuppress the bias of the temperature distribution when applying thevoltage. In particular, the electrical resistivity of the center portionof the electrode section is smaller than that of the expanded portion ofthe electrode section, and hence it is possible to effectively suppressthe bias of the temperature distribution in the cell extending directionof the honeycomb structure. In consequence, it is possible to suppressthe bias of the temperature distribution of the whole honeycombstructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing one embodiment of ahoneycomb structure of the present invention;

FIG. 2 is a schematic view showing a cross section which is parallel toa cell extending direction in the one embodiment of the honeycombstructure of the present invention;

FIG. 3 is a schematic view showing a cross section which isperpendicular to the cell extending direction in the one embodiment ofthe honeycomb structure of the present invention;

FIG. 4 is a front view schematically showing another embodiment of thehoneycomb structure of the present invention;

FIG. 5 is a schematic view showing a cross section cut along the A-A′line of FIG. 4;

FIG. 6 is a side view schematically showing the embodiment of thehoneycomb structure of the present invention;

FIG. 7 is a schematic view showing part of a cross section which isperpendicular to a cell extending direction in another embodiment of thehoneycomb structure of the present invention;

FIG. 8 is a perspective view schematically showing still anotherembodiment of the honeycomb structure of the present invention;

FIG. 9 is a schematic view showing a cross section which is parallel toa cell extending direction in the embodiment of the honeycomb structureof the present invention;

FIG. 10 is a perspective view schematically showing a further embodimentof the honeycomb structure of the present invention;

FIG. 11 is a schematic view showing a cross section which is parallel tothe cell extending direction in the embodiment of the honeycombstructure of the present invention; and

FIG. 12 is a schematic view showing part of a cross section which isperpendicular to the cell extending direction in the embodiment of thehoneycomb structure of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Next, modes for carrying out the present invention will be described indetail with reference to the drawings, but it should be understood thatthe present invention is not limited to the following embodiments, anddesign change, improvement and the like are suitably added based on theordinary knowledge of a person skilled in the art without departing fromthe scope of the present invention.

(1) Honeycomb Structure

As shown in FIG. 1 to FIG. 3, one embodiment of a honeycomb structure ofthe present invention comprises a tubular honeycomb structure section 4including porous partition walls 1 which partition and form a pluralityof cells 2 extending from one end surface 11 to the other end surface 12to become through channels of a fluid, and an outer peripheral wall 3positioned in an outermost periphery; and a pair of electrode sections21 and 21 arranged on a side surface 5 of the honeycomb structuresection 4. An electrical resistivity of the honeycomb structure section4 is from 1 to 200 Ωcm, each of the pair of electrode sections 21 and 21is formed into a band-like shape extending in an extending direction ofthe cells 2 of the honeycomb structure section 4, the one electrodesection 21 in the pair of electrode sections 21 and 21 is disposed on anopposite side of the other electrode section 21 in the pair of electrodesections 21 and 21 via the center O of the honeycomb structure section 4in a cross section which is perpendicular to the extending direction ofthe cells 2, an angle which is 0.5 time as large as a central angle ofeach of the electrode sections 21 and 21 is from 15 to 65° in the crosssection which is perpendicular to the extending direction of the cells2, and each of the electrode sections 21 and 21 is formed so as tobecome thinner from a center portion 21 a in a peripheral directiontoward both ends (the side edges) 21 bb and 21 bb in the peripheraldirection in the cross section which is perpendicular to the extendingdirection of the cells 2. FIG. 1 is a perspective view schematicallyshowing the one embodiment of the honeycomb structure of the presentinvention. FIG. 2 is a schematic view showing a cross section which isparallel to the cell extending direction in the one embodiment of thehoneycomb structure of the present invention. FIG. 3 is a schematic viewshowing a cross section which is perpendicular to the cell extendingdirection in the one embodiment of the honeycomb structure of thepresent invention. It is to be noted that in FIG. 3, the partition wallsare omitted.

Thus, in a honeycomb structure 100 of the present embodiment, theelectrical resistivity of the honeycomb structure section 4 is from 1 to200 Ωcm, and hence even when a current is allowed to flow by using apower source having a high voltage, the current does not excessivelyflow, whereby it is possible to suitably use the honeycomb structure asa heater. Moreover, “each of the pair of electrode sections 21 and 21 isformed into a band-like shape extending in the extending direction ofthe cells 2 of the honeycomb structure section 4, the one electrodesection 21 in the pair of electrode sections 21 and 21 is disposed on anopposite side of the other electrode section 21 in the pair of electrodesections 21 and 21 via the center of the honeycomb structure section 4in a cross section which is perpendicular to the extending direction ofthe cells 2, an angle which is 0.5 time as large as a central angle α ofeach of the electrode sections 21 and 21 (the angle θ of 0.5 time thecentral angle α) is from 15 to 65° in the cross section which isperpendicular to the extending direction of the cells 2”, and hence itis possible to suppress a bias of a temperature distribution of thehoneycomb structure section 4 when applying the voltage across the pairof electrode sections 21 and 21. Furthermore, “each of the electrodesections 21 and 21 is formed so as to become thinner from the centerportion 21 a in a peripheral direction toward both ends (the side edges)21 bb and 21 bb in the peripheral direction in the cross section whichis perpendicular to the extending direction of the cells 2”, and henceit is possible to further suppress the bias of the temperaturedistribution when applying the voltage.

Here, when “the one electrode section 21 in the pair of electrodesections 21 and 21 is disposed on the opposite side of the otherelectrode section 21 in the pair of electrode sections 21 and 21 via thecenter O of the honeycomb structure section 4 in the cross section whichis perpendicular to the extending direction of the cells 2”, it is meantthat the pair of electrode sections 21 and 21 are arranged in thehoneycomb structure section 4 so as to have such a positional relationthat in the cross section which is perpendicular to the extendingdirection of the cells 2, an angle β (the angle around “the center O”)formed by “a line segment connecting the center point of the oneelectrode section 21 (the center point in “the peripheral direction ofthe honeycomb structure section 4”) and the center O of the honeycombstructure section 4” and “a line segment connecting the center point ofthe other electrode section 21 (the center point in “the peripheraldirection of the honeycomb structure section 4”) and the center O of thehoneycomb structure section 4” is in a range of 170 to 190°. Moreover,as shown in FIG. 3, “the central angle α of the electrode section 21” isthe angle formed by two line segments connecting both the ends of theelectrode section 21 and the center O of the honeycomb structure section4 in the cross section which is perpendicular to the cell extendingdirection (the inner angle of the portion of the center O in a shape(e.g., the fan-like shape) formed by “the electrode section 21”, “theline segment connecting one end portion of the electrode section 21 andthe center O”, and “the line segment connecting the other end portion ofthe electrode section 21 and the center O” in the cross section which isperpendicular to the cell extending direction).

Moreover, “the center portion of the electrode section 21 in theperipheral direction in the cross section which is perpendicular to thecell extending direction” means the center portion of the electrodesection 21 in “the peripheral direction of the honeycomb structuresection 4” in the cross section of the honeycomb structure which isperpendicular to the cell extending direction. Furthermore, “the centerportion of the electrode section 21” may be “one center point of theelectrode section 21 in the peripheral direction” in the cross sectionwhich is perpendicular to the cell extending direction, or “a portionpositioned at the center of the electrode section 21 in the peripheraldirection and having a width in the peripheral direction” in the crosssection which is perpendicular to the cell extending direction.Moreover, when “the portion having the width in the peripheral directionis positioned at the center in the peripheral direction”, it is meantthat “the portion having the width in the peripheral direction” isdisposed at a position which overlaps with the center point of theelectrode section 21 in the peripheral direction. In the honeycombstructure of the present embodiment, the center point of the electrodesection 21 in the peripheral direction preferably coincides with thecenter point of “the center portion” of the electrode section 21 in theperipheral direction.

In the honeycomb structure 100 of the present embodiment, as shown inFIG. 1 to FIG. 3, each of the electrode sections 21 and 21 isconstituted of the center portion 21 a in the peripheral direction ofthe honeycomb structure section 4, and expanded portions 21 b and 21 bpositioned on both sides of the center portion 21 a in the peripheraldirection in the cross section which is perpendicular to the cellextending direction, and the electrical resistivity of the centerportion 21 a of the electrode section 21 is smaller than the electricalresistivity of the expanded portion 21 b of the electrode section 21.Since the honeycomb structure 100 of the present embodiment has such aconstitution, it is possible to further suppress the bias of thetemperature distribution when applying the voltage. In particular, sincethe electrical resistivity of the center portion 21 a of the electrodesection 21 is smaller than the electrical resistivity of the expandedportion 21 b of the electrode section 21, it is possible to effectivelysuppress the bias of the temperature distribution in the extendingdirection of the cells 2 of the honeycomb structure section 4. Inconsequence, it is possible to suppress the bias of the temperaturedistribution of the whole honeycomb structure 100. Additionally, in thehoneycomb structure 100 of the present embodiment, the center portion 21a of the electrode section 21 is “the portion positioned at the centerof the electrode section in the peripheral direction and having thewidth in the peripheral direction” in the cross section which isperpendicular to the cell extending direction.

In the honeycomb structure 100 of the present embodiment, a material ofthe partition walls 1 and the outer peripheral wall 3 preferablycontains a silicon-silicon carbide composite material or silicon carbideas a main component, and the material is further preferably thesilicon-silicon carbide composite material or silicon carbide. When “thematerial of the partition walls 1 and the outer peripheral wall 3contains silicon carbide particles and silicon as main components”, itis meant that the partition walls 1 and the outer peripheral wall 3contain 90 mass % of the silicon carbide particles and silicon or morein the whole material. When such a material is used, the electricalresistivity of the honeycomb structure section can be from 1 to 200 Ωcm.Here, the silicon-silicon carbide composite material contains thesilicon carbide particles as aggregates, and silicon as a binder whichbinds the silicon carbide particles, and the plurality of siliconcarbide particles are preferably bound by silicon so as to form poresamong the silicon carbide particles. Moreover, silicon carbide isobtained by sintering the silicon carbide. The electrical resistivity ofthe honeycomb structure section is a value at 400° C.

In the honeycomb structure 100 of the present embodiment, as shown inFIG. 1 to FIG. 3, the pair of electrode sections 21 and 21 are arrangedon the side surface 5 of the honeycomb structure section 4. Thehoneycomb structure 100 of the present embodiment generates heat byapplying the voltage across the pair of electrode sections 21 and 21.The voltage to be applied is preferably from 12 to 900 V, and furtherpreferably from 64 to 600 V.

As shown in FIG. 1 to FIG. 3, each of the pair of electrode sections 21and 21 is formed into “the band-like shape” extending in the extendingdirection of the cells 2 of the honeycomb structure section 4. Moreover,the one electrode section 21 in the pair of electrode sections 21 and 21is disposed on the opposite side of the other electrode section 21 inthe pair of electrode sections 21 and 21 via the center portion O of thehoneycomb structure section 4 in the cross section which isperpendicular to the extending direction of the cells 2. Furthermore,the angle which is 0.5 time as large as the central angle α of each ofthe electrode sections 21 and 21 (the angle θ of 0.5 time the centralangle α) is from 15 to 65° in the cross section which is perpendicularto the extending direction of the cells 2. Thus, the electrode section21 is formed into the band-like shape, a longitudinal direction of theband-like electrode section 21 extends in the extending direction of thecells 2 of the honeycomb structure section 4, the pair of electrodesections 21 and 21 are arranged on the opposite sides via the centerportion O of the honeycomb structure section 4, and the angle θ of 0.5time the central angle α of each of the electrode sections 21 and 21 isfrom 15 to 65° in the cross section which is perpendicular to theextending direction of the cells 2. Therefore, when the voltage isapplied across the pair of electrode sections 21 and 21, it is possibleto suppress the bias of the current flowing through the honeycombstructure section 4, whereby it is possible to suppress the bias of theheat generation in the honeycomb structure section 4.

In the cross section which is perpendicular to the extending directionof the cells 2, an upper limit value of “the angle θ of 0.5 time thecentral angle α” of each of the electrode sections 21 and 21 ispreferably 600, and further preferably 55°. Moreover, in the crosssection which is perpendicular to the extending direction of the cells2, a lower limit value of “the angle θ of 0.5 time the central angle α”of each of the electrode sections 21 and 21 is preferably 200, andfurther preferably 30°. In addition, “the angle θ of 0.5 time thecentral angle α” of the one electrode section 21 has a size which ispreferably from 0.9 to 1.1 times, and further preferably 1.0 time (thesame size) as large as “the angle θ of 0.5 time the central angle α” ofthe other electrode section 21. In consequence, when the voltage isapplied across the pair of electrode sections 21 and 21, it is possibleto suppress the bias of the current flowing through the honeycombstructure section 4, whereby it is possible to suppress the bias of theheat generation in the honeycomb structure section 4.

The electrode section 21 is constituted of the center portion 21 a inthe peripheral direction, and the expanded portions 21 b and 21 bpositioned on both the sides of the center portion 21 a in theperipheral direction in the cross section which is perpendicular to theextending direction of the cells 2, and the electrical resistivity ofthe center portion 21 a of the electrode section 21 is preferablysmaller than the electrical resistivity of the expanded portion 21 b ofthe electrode section 21 (the center portion 21 a comes in contact withthe expanded portion 21 b, and a boundary surface is formed in a contactportion). Thus, the electrical resistivity of the center portion 21 a ofthe electrode section 21 is smaller than the electrical resistivity ofthe expanded portion 21 b of the electrode section 21. Therefore, whenthe voltage is applied across the center portions 21 a and 21 a of theelectrode sections 21 and 21, the current easily flows through thecenter portion 21 a, and the bias of the flow of the current in the cellextending direction of the honeycomb structure decreases. Inconsequence, it is possible to effectively suppress the bias of thetemperature distribution in the extending direction of the cells 2 ofthe honeycomb structure section 4. Moreover, when the current flows fromthe center portion 21 a through the expanded portion 21 b, it ispossible to suppress the bias of the temperature distribution of thewhole honeycomb structure 100.

The electrical resistivity of the center portion 21 a of the electrodesection 21 is preferably from 1 to 60%, and further preferably 15 to 50%of the electrical resistivity of the expanded portion 21 b of theelectrode section 21. When the electrical resistivity is smaller than1%, the flow of the current in an outer peripheral direction of a crosssection which is perpendicular to a central axis of the honeycombstructure section (the peripheral direction in the honeycomb structuresection, and the direction from the center portion 21 a toward theexpanded portion 21 b) decreases, and the bias of the temperaturedistribution increases sometimes. When the electrical resistivity islarger than 60%, the effect of suppressing the bias of the temperaturedistribution of the honeycomb structure 100 deteriorates sometimes.Moreover, the electrical resistivity of the center portion 21 a ispreferably from 0.1 to 10 Ωcm, and further preferably from 0.1 to 2.0Ωcm. When the electrical resistivity is larger than 10 Ωcm, the effectof suppressing the bias of the temperature distribution of the honeycombstructure 100 deteriorates sometimes. When the electrical resistivity issmaller than 0.1 Ωcm, the flow of the current in the outer peripheraldirection of the cross section which is perpendicular to the centralaxis of the honeycomb structure section decreases, and the bias of thetemperature distribution increases sometimes. Furthermore, theelectrical resistivity of the expanded portion 21 b is preferably from0.1 to 100 Ωcm, and further preferably from 0.1 to 50 Ωcm. When theelectrical resistivity is larger than 100 Ωcm, the effect of suppressingthe bias of the temperature distribution of the honeycomb structure 100deteriorates sometimes. When the electrical resistivity is smaller than0.1 Ωcm, the flow of the current in the outer peripheral direction ofthe cross section which is perpendicular to the central axis of thehoneycomb structure section decreases, and the bias of the temperaturedistribution increases sometimes. The electrical resistivity of theelectrode section 21 (the center portion 21 a and the expanded portion21 b) is a value at 400° C.

In the honeycomb structure 100 of the present embodiment, as shown inFIG. 1 and FIG. 3, the electrode section 21 includes a portion whichbecomes a boundary (the boundary surface) S between the center portion21 a and the expanded portion 21 b. Therefore, in the honeycombstructure 100 of the present embodiment, the respective electrodesections 21 and 21 include the portions S which become the boundaries,and are not continuously formed in the cross section which isperpendicular to the cell extending direction. The “boundary portion(the boundary surface) S” in the electrode section is a portion wherethe center portion 21 a comes in contact with the expanded portion 21 b.The electrode section comes in contact, but has a discontinuousstructure in this portion (the boundary portion (the boundary surface)S). It can be considered that in the electrode section, a continuity(the integrity) of “material characteristics such as a material qualityand a porosity” is discontinued in the boundary portion (the boundarysurface) S (between the center portion 21 a and the expanded portion 21b).

The expanded portion 21 b of the electrode section 21 is formed so as tobecome thinner from an end portion 21 ba which comes in contact with thecenter portion 21 a toward a side edge 21 bb which is an end portion(the peripheral edge) on the opposite side in the cross section which isperpendicular to the extending direction of the cells 2. When thevoltage is applied across the electrode sections 21 and 21, thehoneycomb structure 100 has the tendency that the current flows mostthrough the vicinity of the side edge 21 bb of the expanded portion 21 bof the electrode section 21, to raise a temperature. However, when theexpanded portion 21 b is “formed so as to become thinner from the endportion 21 ba which comes in contact with the center portion 21 a towardthe side edge 21 bb in the cross section which is perpendicular to theextending direction of the cells 2”, the temperature of “the vicinity ofthe side edge 21 bb of the expanded portion 21 b of the electrodesection 21” of the honeycomb structure 100 is lowered, whereby it ispossible to decrease the bias of the temperature distribution. In thisway, the temperature of a high temperature portion of the honeycombstructure when applying the voltage is lowered, whereby the bias of thetemperature distribution of the honeycomb structure decreases, and thetemperature distribution becomes more even.

The expanded portion 21 b is preferably formed so as to gradually becomethinner continuously “from the end portion 21 ba which comes in contactwith the center portion 21 a toward the side edge 21 bb in the crosssection which is perpendicular to the extending direction of the cells2” as in the honeycomb structure 100 shown in FIG. 3. However, theexpanded portion may be formed so as to become thinner stepwise as in ahoneycomb structure 300 shown in FIG. 7. In the honeycomb structure 300shown in FIG. 7, an expanded portion 21 b becomes thinner stepwise “fromthe end portion 21 ba which comes in contact with the center portion 21a toward the side edge 21 bb in the cross section which is perpendicularto the extending direction of the cells 2”, and specifically, theexpanded portion becomes thinner stepwise in order of a region A, aregion B, and a region C. Conditions of the honeycomb structure 300 ofthe present embodiment are preferably the same as conditions in the oneembodiment (the honeycomb structure 100) of the honeycomb structure ofthe present invention, except that the expanded portion 21 b of theelectrode section 21 is formed so as to become thinner stepwise “fromthe end portion 21 ba which comes in contact with the center portion 21a toward the side edge 21 bb in the cross section which is perpendicularto the extending direction of the cells 2” as described above. FIG. 7 isa schematic view showing part of the cross section which isperpendicular to the cell extending direction in the embodiment of thehoneycomb structure of the present invention. In FIG. 7, partition wallsare omitted.

A thickness of a portion of the expanded portion 21 b which comes incontact with the center portion 21 a is preferably from 40 to 100%, andfurther preferably from 60 to 80% of a thickness of the center portion21 a. When the thickness is smaller than 40%, the current does noteasily flow through the expanded portion 21 b, and the effect ofdecreasing the bias of the temperature distribution of the honeycombstructure deteriorates sometimes. The thickness of the side edge 21 bbof the expanded portion 21 b is preferably from 5 to 80%, and furtherpreferably from 10 to 50% of the thickness of the center portion 21 a.

The thickness of the center portion 21 a of the electrode section 21 ispreferably from 0.2 to 5 mm, and further preferably from 2 to 5 mm. Whenthe thickness is smaller than 0.2 mm, the effect of decreasing the biasof the temperature distribution when applying the voltage to thehoneycomb structure deteriorates sometimes. When the thickness is largerthan 5 mm, the honeycomb structure is not easily inserted when insertingthe structure into a tubular can member.

As shown in FIG. 1 and FIG. 2, in the honeycomb structure 100 of thepresent embodiment, each of the pair of electrode sections 21 and 21 isformed into the band-like shape extending in the extending direction ofthe cells 2 of the honeycomb structure section 4 and “extending overboth end portions (over both the end surfaces 11 and 12)”. Thus, whenthe pair of electrode sections 21 and 21 are arranged over both the endportions of the honeycomb structure section 4, it is possible to moreeffectively suppress the bias of the current flowing through thehoneycomb structure section 4 when applying the voltage across the pairof electrode sections 21 and 21, whereby it is possible to moreeffectively suppress the bias of the heat generation in the honeycombstructure section 4. Here, when “the electrode section 21 is formed(disposed) so as to extend over both the end portions of the honeycombstructure section 4”, it is meant that one end portion of the electrodesection 21 comes in contact with one end portion (one end surface) ofthe honeycomb structure section 4 and that the other end portion of theelectrode section 21 comes in contact with the other end portion (theother end surface) of the honeycomb structure section 4.

The pair of electrode sections 21 and 21 are preferably formed so as toextend over both the end portions of the honeycomb structure section 4from the viewpoint that “the bias of the current flowing through thehoneycomb structure section 4 is more effectively suppressed, therebymore effectively suppressing the bias of the heat generation in thehoneycomb structure section 4” as described above. On the other hand, asshown in FIG. 8 and FIG. 9, both end portions 21 c and 21 d of theelectrode section 21 in “the extending direction of the cells 2 of thehoneycomb structure section 4” do not come in contact with (do notreach) both end portions (both the end surfaces 11 and 12) of thehoneycomb structure section 4, and this state is also a preferableconfiguration. Moreover, the one end portion 21 c of the electrodesection 21 comes in contact with (reaches) the one end portion (the oneend surface 11) of the honeycomb structure section 4, the other endportion 21 d does not come in contact with (does not reach) the otherend portion (the other end surface 12) of the honeycomb structuresection 4, and this state is also a preferable configuration. When atleast one end portion of the electrode section 21 does not come incontact with (does not reach) the end portion (the end surface) of thehoneycomb structure section 4, it is possible to enhance a thermal shockresistance of the honeycomb structure. That is each of the pair ofelectrode sections 21 and 21 preferably has the constitution where atleast one end portion does not come in contact with (does not reach) theend portion (the end surface) of the honeycomb structure section 4 fromthe viewpoint of “enhancing the thermal shock resistance of thehoneycomb structure”. From the above, when it is considered that theviewpoint that “the bias of the current flowing through the honeycombstructure section 4 is more effectively suppressed, thereby moreeffectively suppressing the bias of the heat generation in the honeycombstructure section 4” is important, the pair of electrode sections 21 and21 are preferably formed so as to extend over both the end portions ofthe honeycomb structure section 4. When it is considered that theviewpoint of “enhancing the thermal shock resistance of the honeycombstructure” is important, at least one end portion of each of the pair ofelectrode sections 21 and 21 preferably does not come in contact with(does not reach) the end portion (the end surface) of the honeycombstructure section 4.

Moreover, a distance from the one end portion 21 c of the one electrodesection 21 in the pair of electrode sections 21 and 21 to “the one endportion (the one end surface 11) of the honeycomb structure section 4”is preferably the same as a distance from the one end portion 21 c ofthe remaining electrode section 21 in the pair of electrode sections 21and 21 to “the one end portion (the one end surface 11) of the honeycombstructure section 4”, but the distances may be different. Furthermore, adistance from the other end portion 21 d of the one electrode section 21in the pair of electrode sections 21 and 21 to “the other end portion(the other end surface 12) of the honeycomb structure section 4” ispreferably the same as a distance from the other end portion 21 d of theremaining electrode section 21 in the pair of electrode sections 21 and21 to “the other end portion (the other end surface 12) of the honeycombstructure section 4”, but the distances may be different. Additionally,the one end portion 21 c of the electrode section 21 faces the one endportion (the one end surface 11) side of the honeycomb structure section4, and the other end portion 21 d of the electrode section 21 faces theother end portion (the other end surface 12) side of the honeycombstructure section 4. FIG. 8 is a perspective view schematically showingstill another embodiment (a honeycomb structure 400) of the honeycombstructure of the present invention. FIG. 9 is a schematic view showing across section which is parallel to a cell extending direction in theembodiment (the honeycomb structure 400) of the honeycomb structure ofthe present invention. Conditions of the honeycomb structure 400 of thepresent embodiment are preferably the same as conditions of the oneembodiment (the honeycomb structure 100) of the honeycomb structure ofthe present invention, except that at least one end portion of theelectrode section 21 does not come in contact with (does not reach) theend portion (the end surface) of the honeycomb structure section 4.

When at least one end portion of the electrode section 21 does not comein contact with (does not reach) the end portion (the end surface) ofthe honeycomb structure section 4, a distance between “the end portionof the electrode section 21” and “the end portion (the end surface) ofthe honeycomb structure section”, which do not come in contact with eachother, is preferably 50% or smaller, and further preferably 25% orsmaller than a length of the honeycomb structure section 4 in theextending direction of the cells 2. When the distance is larger than50%, the bias of the current flowing through the honeycomb structuresection 4 is not easily suppressed sometimes, when applying the voltageacross the pair of electrode sections 21 and 21.

In the honeycomb structure 100 of the present embodiment, when the angleof 0.5 time the central angle of the center portion 21 a of theelectrode section 21 is preferably from 5 to 25° in the cross sectionwhich is perpendicular to the cell extending direction. When the angleis smaller than 5°, the effect of decreasing the bias of the temperaturedistribution in the cell extending direction of the honeycomb structurewhen applying the voltage to the honeycomb structure deterioratessometimes. When the angle is larger than 25°, the effect of lowering thetemperature around the side edge 21 bb of the expanded portion 21 b ofthe electrode section 21 of the honeycomb structure 100 deterioratessometimes.

In the honeycomb structure 100 of the present embodiment, when thecenter point of the electrode section 21 in the peripheral direction(the peripheral direction of the honeycomb structure section) is aposition of “0°” and the side edge 21 bb of the electrode section 21 isa position of “the angle θ of 0.5 time the central angle α of theelectrode section 21” (the position of the angle θ) in the cross sectionwhich is perpendicular to the cell extending direction, a thickness ofthe electrode section 21 at a position of “0.5 time the angle θ (0.5θ)”(the position rotated as much as 0.5θ in the peripheral direction from“the position of 0°” toward “the position of the angle θ” (the midpointbetween “the position of 0°” and “the position of the angle θ”)) ispreferably 95% or smaller, further preferably from 10 to 90%, andespecially preferably from 15 to 85% of the thickness of the electrodesection 21 at the center point in the peripheral direction. When thethickness is larger than 95%, the effect of suppressing the bias of thetemperature distribution when applying the voltage to the honeycombstructure deteriorates sometimes.

Moreover, in the honeycomb structure 100 of the present embodiment, athickness of the electrode section 21 at a position of “0.8 time theangle θ (0.8θ)” is preferably 80% or smaller, further preferably from0.5 to 75%, and especially preferably from 1 to 65% of the thickness ofthe electrode section 21 at the center point in the peripheraldirection, in the cross section which is perpendicular to the cellextending direction. When the thickness is larger than 80%, the effectof suppressing the bias of the temperature distribution when applyingthe voltage to the honeycomb structure deteriorates sometimes.

The honeycomb structure 100 of the present embodiment further preferablysatisfies conditions of both the thickness of the electrode section atthe above “position of 0.5θ” and the thickness of the electrode sectionat the above “position of 0.8θ”.

The center portion 21 a and the expanded portion 21 b of the electrodesection 21 preferably contain silicon carbide particles and silicon asmain components, and are further preferably formed by using the siliconcarbide particles and silicon as raw materials except usually containedimpurities. Here, when “the silicon carbide particles and silicon areused as the main components”, it is meant that a total mass of thesilicon carbide particles and silicon is 90 mass % or larger than a massof the whole electrode section. Thus, when the electrode section 21contains the silicon carbide particles and silicon as the maincomponents, the component of the electrode section 21 is the same as orclose to the component of the honeycomb structure section 4 (when thematerial of the honeycomb structure section is silicon carbide), so thata thermal expansion coefficient of the electrode section 21 is the sameas or close to that of the honeycomb structure section 4. Moreover,since the materials are the same or close, a joining strength betweenthe electrode section 21 and the honeycomb structure section 4 alsoincreases. Therefore, even when heat stress is applied to the honeycombstructure, the electrode section 21 can be prevented from peeling fromthe honeycomb structure section 4, or a joined portion between theelectrode section 21 and the honeycomb structure section 4 can beprevented from being broken.

When the center portion 21 a of the electrode section 21 contains thesilicon carbide particles and silicon as the main components, a ratio ofa mass of silicon contained in the center portion 21 a of the electrodesection 21 to “the total of the masses of the silicon carbide particlesand silicon” contained in the center portion 21 a of the electrodesection 21 is preferably from 20 to 50 mass %, and further preferablyfrom 30 to 45 mass %. In consequence, the electrical resistivity of thecenter portion 21 a of the electrode section 21 can be in a range of 0.1to 10 Ωcm. When the ratio is smaller than 20 mass %, the electricalresistivity increases, a strength to bind silicon carbide deteriorates,and the center portion 21 a easily deteriorates sometimes.

When the expanded portion 21 b of the electrode section 21 contains thesilicon carbide particles and silicon as the main components, a ratio ofa mass of silicon contained in the expanded portion 21 b of theelectrode section 21 to “the total of the masses of the silicon carbideparticles and silicon” contained in the expanded portion 21 b of theelectrode section 21 is preferably from 20 to 40 mass %, and furtherpreferably from to 35 mass %. In consequence, the electrical resistivityof the expanded portion 21 b of the electrode section 21 can be in arange of 0.1 to 100 Ωcm. When the ratio is smaller than 20 mass %, theelectrical resistivity increases, the strength to bind silicon carbidedeteriorates, and the expanded portion 21 b easily deterioratessometimes.

When the main components of the center portion 21 a of the electrodesection 21 are the silicon carbide particles and silicon, an averageparticle diameter of the silicon carbide particles contained in thecenter portion 21 a is preferably from 10 to 60 μm, and furtherpreferably from 20 to 60 μm. When the average particle diameter of thesilicon carbide particles contained in the center portion 21 a is insuch a range, the electrical resistivity of the center portion 21 a canbe in a range of 0.1 to 10 Ωcm. When an average pore diameter of thesilicon carbide particles contained in the center portion 21 a issmaller than 10 μm, the electrical resistivity of the center portion 21a excessively increases sometimes. When the average pore diameter of thesilicon carbide particles contained in the center portion 21 a is largerthan 60 μm, the strength of the center portion 21 a decreases, and theportion easily breaks sometimes. The average particle diameter of thesilicon carbide particles contained in the center portion 21 a is avalue measured by a laser diffraction process.

When the main components of the expanded portion 21 b of the electrodesection 21 are the silicon carbide particles and silicon, the averageparticle diameter of the silicon carbide particles contained in theexpanded portion 21 b is preferably from 10 to 60 μm, and furtherpreferably from 20 to 60 μm. When the average particle diameter of thesilicon carbide particles contained in the expanded portion 21 b is insuch a range, the electrical resistivity of the expanded portion 21 bcan be in a range of 0.1 to 100 Ωcm. When the average pore diameter ofthe silicon carbide particles contained in the expanded portion 21 b issmaller than 10 μm, the electrical resistivity of the expanded portion21 b excessively increases sometimes. When the average pore diameter ofthe silicon carbide particles contained in the expanded portion 21 b islarger than 60 μm, the strength of the expanded portion 21 b decreases,and the portion easily breaks sometimes. The average particle diameterof the silicon carbide particles contained in the expanded portion 21 bis preferably the same as the average particle diameter of the siliconcarbide particles contained in the center portion. The average particlediameter of the silicon carbide particles contained in the expandedportion 21 b is the value measured by the laser diffraction process.

Porosities of the center portion 21 a and the expanded portion 21 b ofthe electrode section 21 are preferably from 30 to 60%, and furtherpreferably from 30 to 55%. When the porosities of the center portion 21a and expanded portion 21 b of the electrode section 21 are in such arange, a suitable electrical resistivity can be obtained. When theporosities of the center portion 21 a and the expanded portion 21 b ofthe electrode section 21 are smaller than 30%, the portions are deformedsometimes during manufacturing. When the porosities are larger than 60%,the electrical resistivity excessively increases sometimes. Theporosities are values measured by a mercury porosimeter.

The average pore diameters of the center portion 21 a and the expandedportion 21 b of the electrode section 21 are preferably from 5 to 45 μm,and further preferably from 7 to 40 μm. When the average pore diametersof the center portion 21 a and the expanded portion 21 b of theelectrode section 21 are in such a range, the suitable electricalresistivity can be obtained. When the average pore diameters of thecenter portion 21 a and the expanded portion 21 b of the electrodesection 21 are smaller than 5 μm, the electrical resistivities of thecenter portion 21 a and the expanded portion 21 b excessively increasesometimes. When the average pore diameters are larger than 45 μm, thestrengths of the center portion 21 a and the expanded portion 21 b ofthe electrode section 21 decrease, and the portions easily breaksometimes. The average pore diameters are the values measured by themercury porosimeter.

Partition wall thicknesses of the honeycomb structure 100 of the presentembodiment are from 50 to 200 μm, and preferably from 70 to 130 μm. Whenthe partition wall thicknesses are in such a range, it is possible toprevent a pressure loss from excessively increasing when allowing anexhaust gas to flow, even in a case where the honeycomb structure 100 isused as a catalyst carrier and a catalyst is loaded onto the structure.When the partition wall thicknesses are smaller than 50 μm, the strengthof the honeycomb structure deteriorates sometimes. When the partitionwall thicknesses are larger than 200 μm, the pressure loss when allowingthe exhaust gas to flow increases sometimes, in the case where thehoneycomb structure 100 is used as the catalyst carrier and the catalystis loaded onto the structure.

In the honeycomb structure 100 of the present embodiment, a cell densityis preferably from 40 to 150 cells/cm², and further preferably from 70to 100 cells/cm². When the cell density is in such a range, apurification performance of the catalyst can be enhanced in a statewhere the pressure loss when allowing the exhaust gas to flow isdecreased. When the cell density is smaller than cells/cm², a catalystloading area decreases sometimes. When the cell density is larger than150 cells/cm, the pressure loss when allowing the exhaust gas to flowincreases sometimes, in the case where the honeycomb structure 100 isused as the catalyst carrier and the catalyst is loaded onto thestructure.

In the honeycomb structure 100 of the present embodiment, the averageparticle diameter of the silicon carbide particles (the aggregates)constituting the honeycomb structure section 4 is from 3 to 50 μm, andpreferably from 3 to 40 μm. When the average particle diameter of thesilicon carbide particles constituting the honeycomb structure section 4is in such a range, the electrical resistivity of the honeycombstructure section 4 at 400° C. can be from 1 to 200 Ωcm. When theaverage particle diameter of the silicon carbide particles is smallerthan 3 μm, the electrical resistivity of the honeycomb structure section4 increases sometimes. When the average particle diameter of the siliconcarbide particles is larger than 50 μm, the electrical resistivity ofthe honeycomb structure section 4 decreases sometimes. Furthermore, whenthe average particle diameter of the silicon carbide particles is largerthan 50 μm, an extruding die is clogged with a forming raw materialsometimes at the extruding of a honeycomb formed body. The averageparticle diameter of the silicon carbide particles is the value measuredby the laser diffraction process.

In the honeycomb structure 100 of the present embodiment, the electricalresistivity of the honeycomb structure section 4 is from 1 to 200 Ωcm,and preferably from 10 to 100 Ωcm. When the electrical resistivity issmaller than 1 Ωcm, the current excessively flows sometimes, forexample, in a case where the honeycomb structure 100 is energized by apower source having a high voltage of 200 V or larger (the voltage isnot limited to 200 V). When the electrical resistivity is larger than200 Ωcm, the current does not easily flow, and the heat is notsufficiently generated sometimes, for example, in the case where thehoneycomb structure 100 is energized by the power source having a highvoltage of 200 V or larger (the voltage is not limited to 200 V). Theelectrical resistivity of the honeycomb structure section is a valuemeasured by a four-terminal process.

In the honeycomb structure 100 of the present embodiment, the electricalresistivity of the expanded portion 21 b of the electrode section 21 ispreferably smaller than the electrical resistivity of the honeycombstructure section 4. Furthermore, the electrical resistivity of theexpanded portion 21 b of the electrode section 21 is further preferably20% or smaller, and especially preferably from 1 to 10% of theelectrical resistivity of the honeycomb structure section 4. When theelectrical resistivity of the expanded portion 21 b of the electrodesection 21 is 20% or smaller than the electrical resistivity of thehoneycomb structure section 4, the expanded portion 21 b of theelectrode section 21 more effectively functions as an electrode.

In the honeycomb structure 100 of the present embodiment, when thematerial of the honeycomb structure section 4 is the silicon-siliconcarbide composite material, a ratio of “the mass of silicon as thebinder” contained in the honeycomb structure section 4 to the total of“the mass of the silicon carbide particles as the aggregates” containedin the honeycomb structure section 4 and “the mass of silicon as thebinder” contained in the honeycomb structure section 4 is preferablyfrom 10 to 40 mass %, and further preferably from 15 to 35 mass %. Whenthe ratio is smaller than 10 mass %, the strength of the honeycombstructure deteriorates sometimes. When the ratio is larger than 40 mass%, a shape cannot be held at firing.

The porosities of the partition walls 1 of the honeycomb structuresection 4 are preferably from 35 to 60%, and further preferably from 35to 45%. When the porosities are smaller than 35%, the deformation at thefiring increases sometimes. When the porosities are in excess of 60%,the strength of the honeycomb structure deteriorates sometimes. Theporosities are the values measured by the mercury porosimeter.

The average pore diameter of the partition walls 1 of the honeycombstructure section 4 is preferably from 2 to 15 μm, and furtherpreferably from 4 to 8 μm. When the average pore diameter is smallerthan 2 μm, the electrical resistivity excessively increases sometimes.When the average pore diameter is larger than 15 μm, the electricalresistivity excessively decreases sometimes. The average pore diameteris the value measured by the mercury porosimeter.

Moreover, a thickness of the outer peripheral wall 3 constituting theoutermost periphery of the honeycomb structure 100 of the presentembodiment is preferably from 0.1 to 2 mm. When the thickness is smallerthan 0.1 mm, the strength of the honeycomb structure 100 deterioratessometimes. When the thickness is larger than 2 mm, an area of thepartition walls onto which the catalyst is loaded decreases sometimes.

In the honeycomb structure 100 of the present embodiment, a shape of thecells 2 in the cross section which is perpendicular to the extendingdirection of the cells 2 is preferably a quadrangular shape, a hexagonalshape, an octagonal shape, or a combination thereof. When the cells areformed into such a shape, the pressure loss when allowing the exhaustgas to flow through the honeycomb structure 100 decreases, and thepurification performance of the catalyst enhances.

There is not any special restriction on a shape of the honeycombstructure of the present embodiment, and the shape can be, for example,a tubular shape with a round bottom surface (the cylindrical shape), atubular shape with an oval bottom surface, or a tubular shape with apolygonal (quadrangular, pentangular, hexagonal, heptagonal, oroctagonal) bottom surface. Moreover, as to a size of the honeycombstructure, an area of the bottom surface is preferably from 2000 to20000 mm², and further preferably from 4000 to 10000 mm². Moreover, alength of the honeycomb structure in a central axis direction ispreferably from 50 to 200 mm, and further preferably from 75 to 150 mm.

An isostatic strength of the honeycomb structure 100 of the presentembodiment is preferably 1 MPa or larger, and further preferably 3 MPaor larger. The isostatic strength preferably has a larger value, butwhen a material, a constitution and the like of the honeycomb structure100 are taken into consideration, an upper limit is about 6 MPa. Whenthe isostatic strength is smaller than 1 MPa, the honeycomb structureeasily breaks sometimes during use as the catalyst carrier or the like.The isostatic strength is a value measured by applying a hydrostaticpressure in water.

Next, still another embodiment of the present invention will bedescribed. As shown in FIG. 4 to FIG. 6, a honeycomb structure 200 ofthe present embodiment has a constitution where electrode terminalprotruding portions 22 and 22 to which electric wirings are fastened arearranged at center positions of center portions 21 a and 21 a ofelectrode sections 21 and 21 in a cell extending direction in thehoneycomb structure 100 of the above present invention (see FIG. 1 toFIG. 3). The electrode terminal protruding portion 22 is a portion towhich the wiring from a power source is connected, to apply a voltageacross the electrode sections 21 and 21. Thus, when the electrodeterminal protruding portions 22 and 22 to which the electric wirings arefastened are arranged at “the center positions” of the center portions21 a and 21 a of the electrode sections 21 and 21 in the cell extendingdirection, whereby it is possible to further decrease a bias of atemperature distribution of a honeycomb structure section when applyingthe voltage to the electrode section. FIG. 4 is a front viewschematically showing the embodiment of the honeycomb structure of thepresent invention. FIG. 5 is a schematic view showing a cross sectioncut along the A-A′ line of FIG. 4. FIG. 6 is a side view schematicallyshowing the embodiment of the honeycomb structure of the presentinvention.

Conditions of the honeycomb structure 200 of the present embodiment arepreferably the same as the conditions of the one embodiment (thehoneycomb structure 100) of the honeycomb structure of the presentinvention, except that “the electrode terminal protruding portion 22 and22 to which the electric wirings are fastened are arranged at the centerpositions of the center portions 21 a and 21 a of the electrode sections21 and 21 in the cell extending direction”.

When the main components of the center portion 21 a of the electrodesection 21 are silicon carbide particles and silicon, the maincomponents of the electrode terminal protruding portion 22 arepreferably the silicon carbide particles and silicon. Thus, when theelectrode terminal protruding portion 22 contains the silicon carbideparticles and silicon as the main components, the components of thecenter portion 21 a of the electrode section 21 are the same as (orclose to) the components of the electrode terminal protruding portion22, a thermal expansion coefficient of the center portion 21 a of theelectrode section 21 has a value which is the same as (close to) that ofa thermal expansion coefficient of the electrode terminal protrudingportion 22. Moreover, since the material is the same (or close), ajoining strength between the center portion 21 a of the electrodesection 21 and the electrode terminal protruding portion 22 increases.Therefore, even when heat stress is applied to the honeycomb structure,the electrode terminal protruding portion 22 can be prevented frompeeling from the center portion 21 a of the electrode section 21, or ajoined portion between the electrode terminal protruding portion 22 andthe center portion 21 a of the electrode section 21 can be preventedfrom being broken. Here, when “the electrode terminal protruding portion22 contains the silicon carbide particles and silicon as the maincomponents”, it is meant that a total mass of the silicon carbideparticles and silicon contained in the electrode terminal protrudingportion 22 is 90 mass % or larger than the whole protruding portion.

There is not any special restriction on a shape of the electrodeterminal protruding portion 22, and the protruding portion may be formedinto any shape as long as the protruding portion is joined to the centerportion 21 a of the electrode section 21 and the electric wiring can bejoined to the protruding portion. For example, as shown in FIG. 4 toFIG. 6, the electrode terminal protruding portion 22 preferably has ashape formed by disposing a columnar protruding portion 22 b on aquadrangular plate-like substrate 22 a. When the electrode terminalprotruding portion is formed into such a shape, the electrode terminalprotruding portion 22 can firmly be joined to the center portion 21 a ofthe electrode section 21 via the substrate 22 a, and the electric wiringcan firmly joined to the protruding portion via the protruding portion22 b.

In the electrode terminal protruding portion 22, a thickness of thesubstrate 22 a is preferably from 1 to 5 mm. When the substrate has sucha thickness, the electrode terminal protruding portion 22 can securelybe joined to the center portion 21 a of the electrode section 21. Whenthe thickness is smaller than 1 mm, the substrate 22 a weakens, and theprotruding portion 22 b is easily detached from the substrate 22 asometimes. When the thickness is larger than 5 mm, a space to disposethe honeycomb structure becomes larger than necessary sometimes.

In the electrode terminal protruding portion 22, a length (the width) ofthe substrate 22 a “in an outer peripheral direction of a cross sectionof a honeycomb structure section 4 which is perpendicular to a cellextending direction” is preferably from 10 to 50%, and furtherpreferably from 20 to 40% of a length of the electrode section 21 “inthe outer peripheral direction of the cross section of the honeycombstructure section 4 which is perpendicular to the cell extendingdirection”. When the length is in such a range, the electrode terminalprotruding portion 22 is not easily detached from the center portion 21a of the electrode section 21. When the length is smaller than 10%, theelectrode terminal protruding portion 22 is easily detached from thecenter portion 21 a of the electrode section 21. When the length islarger than 50%, a mass increases sometimes. In the electrode terminalprotruding portion 22, the length of the substrate 22 a in “the cellextending direction” is preferably from 5 to 30% of the length of thehoneycomb structure section 4 in the cell extending direction. When thelength of the substrate 22 a in “the cell extending direction” is insuch a range, a sufficient joining strength can be obtained. When thelength of the substrate 22 a in “the cell extending direction” issmaller than 5% of the length of the honeycomb structure section 4 inthe cell extending direction, the protruding portion is easily detachedfrom the center portion 21 a of the electrode section 21 sometimes.Moreover, when the length is larger than 30%, the mass increasessometimes.

In the electrode terminal protruding portion 22, a thickness of theprotruding portion 22 b is preferably from 3 to 15 mm. When such athickness is set, the electric wiring can securely be joined to theprotruding portion 22 b. protruding When the thickness is smaller than 3mm, the portion 22 b is easily broken sometimes. When the thickness islarger than 15 mm, the electric wiring is not easily connectedsometimes. Moreover, a length of the protruding portion 22 b ispreferably from 3 to 20 mm. When such a length is set, the electricwiring can securely be joined to the protruding portion 22 b. When thelength is smaller than 3 mm, the electric wiring is not easily joinedsometimes. When the length is larger than 20 mm, the protruding portion22 b is easily broken sometimes.

An electrical resistivity of the electrode terminal protruding portion22 is preferably from 0.1 to 2.0 Ωcm, and further preferably from 0.1 to1.0 Ωcm. When the electrical resistivity of the electrode terminalprotruding portion 22 is in such a range, a current can efficiently besupplied to the electrode section 21 through the electrode terminalprotruding portion 22 in a pipe through which a high-temperature exhaustgas flows. When the electrical resistivity of the electrode terminalprotruding portion 22 is larger than 2.0 Ωcm, the current does noteasily flow, and hence the current is not easily supplied to theelectrode section 21 sometimes.

A porosity of the electrode terminal protruding portion 22 is preferablyfrom 30 to 45%, and further preferably from 30 to 40%. When the porosityof the electrode terminal protruding portion 22 is in such a range, asuitable electrical resistivity can be obtained. When the porosity ofthe electrode terminal protruding portion 22 is larger than 45%, thestrength of the electrode terminal protruding portion 22 deterioratessometimes, and especially when the strength of the protruding portion 22b deteriorates, the protruding portion 22 b is easily broken sometimes.The porosity is the value measured by the mercury porosimeter.

An average pore diameter of the electrode terminal protruding portion 22is preferably from 5 to 20 μm, and further preferably from 7 to 15 μm.When the average pore diameter of the electrode terminal protrudingportion 22 is in such a range, the suitable electrical resistivity canbe obtained. When the average pore diameter of the electrode terminalprotruding portion 22 is larger than 20 μm, the strength of theelectrode terminal protruding portion 22 deteriorates sometimes, andespecially when the strength of the protruding portion 22 bdeteriorates, the protruding portion 22 b is easily broken sometimes.The average pore diameter is the value measured by the mercuryporosimeter.

When main components of the electrode terminal protruding portion 22 aresilicon carbide particles and silicon, an average particle diameter ofthe silicon carbide particles contained in the electrode terminalprotruding portion 22 is preferably from 10 to 60 μm, and furtherpreferably from 20 to 60 μm. When the average particle diameter of thesilicon carbide particles contained in the electrode terminal protrudingportion 22 is in such a range, the electrical resistivity of theelectrode terminal protruding portion 22 can be from 0.1 to 2.0 Ωcm.When the average pore diameter of the silicon carbide particlescontained in the electrode terminal protruding portion 22 is smallerthan 10 μm, the electrical resistivity of the electrode terminalprotruding portion 22 excessively increases sometimes. When the averagepore diameter of the silicon carbide particles contained in theelectrode terminal protruding portion 22 is larger than 60 μm, theelectrical resistivity of the electrode terminal protruding portion 22excessively decreases sometimes. The average particle diameter of thesilicon carbide particles contained in the electrode terminal protrudingportion 22 is the value measured by a laser diffraction process.

A ratio of a mass of silicon contained in the electrode terminalprotruding portion 22 to “a total of masses of the silicon carbideparticles and silicon” contained in the electrode terminal protrudingportion 22 is preferably from 20 to 40 mass %, and further preferablyfrom 25 to 35 mass %. When a ratio of the mass of silicon to the totalof the masses of the silicon carbide particles and silicon contained inthe electrode terminal protruding portion 22 is in such a range, anelectrical resistivity of 0.1 to 2.0 Ωcm can easily be obtained. Whenthe ratio of the mass of silicon to the total of the masses of thesilicon carbide particles and silicon contained in the electrodeterminal protruding portion 22 is smaller than 20 mass %, the electricalresistivity excessively increases sometimes. Moreover, when the ratio islarger than 40 mass %, the protruding portion is deformed sometimesduring manufacturing.

Next, a further embodiment of the honeycomb structure of the presentinvention will be described. As shown in FIG. 10 to FIG. 12, a honeycombstructure 500 of the present embodiment has a constitution whereelectrode sections 21 and 21 do not have any boundary portions and arecontinuously formed in a cross section which is perpendicular to a cellextending direction in the honeycomb structure 100 of the above presentinvention (see FIG. 1 to FIG. 3). That is, in the honeycomb structure500 of the present embodiment, the electrode section 21 does not have “aportion which becomes a boundary” formed in a portion where a centerportion 21 a comes in contact with the expanded portion 21 b (see FIG.1). Here, when the electrode section 21 “does not have any boundaryportions and is continuously formed”, it is meant that the electrodesection 21 does not have a discontinuous portion (the portion whichbecomes the boundary (the boundary surface)) where a continuity (theintegrity) of a material quality is discontinued and that a homogeneousstate is present in the electrode section. The discontinuous portionwhere the continuity (the integrity) of “material characteristics suchas the material quality and a porosity” is discontinued is the boundarysurface (the portion which becomes the boundary).

FIG. 10 is a perspective view schematically showing a still furtherembodiment of the honeycomb structure of the present invention. FIG. 11is a schematic view showing a cross section which is parallel to a cellextending direction in the embodiment of the honeycomb structure of thepresent invention. FIG. 12 is a schematic view showing part of a crosssection which is perpendicular to the cell extending direction in theembodiment of the honeycomb structure of the present invention. In FIG.12, partition walls are omitted.

In the honeycomb structure 500 of the present embodiment, the respectiveelectrode sections 21 and 21 do not have any boundary portions and arecontinuously formed in the cross section which is perpendicular to thecell extending direction, and hence a structural strength isadvantageously high. Moreover, since the honeycomb structure 500 of thepresent embodiment has such an electrode section structure,manufacturing steps during the preparation of the electrode section canbe decreased, and manufacturing time can be shortened.

As shown in FIG. 12, each of the electrode sections 21 and 21 in thehoneycomb structure 500 of the present embodiment becomes thinner fromthe center portion 21 a in a peripheral direction toward both ends (boththe peripheral edges) 21 bb and 21 bb in the peripheral direction in thecross section which is perpendicular to the cell extending direction.Moreover, each of the electrode sections 21 and 21 may gradually becomethinner (continuously become thinner) from the center portion 21 a inthe peripheral direction toward both the ends (both the peripheraledges) 21 bb and 21 bb in the peripheral direction in the cross sectionwhich is perpendicular to the cell extending direction (see FIG. 12), ormay become thinner stepwise (become thinner intermittently).

In the honeycomb structure 500 of the present embodiment, “the centerportion 21 a in the peripheral direction (the center portion)” of theelectrode section 21 may be “one point at the center in the peripheraldirection” in the cross section which is perpendicular to the cellextending direction, or may be “a portion positioned at the center inthe peripheral direction and having a width in the peripheral direction”in the cross section which is perpendicular to the cell extendingdirection. When “the center portion 21 a in the peripheral direction(the center portion)” of the electrode section 21 is “the portionpositioned at the center in the peripheral direction and having thewidth in the peripheral direction” in the cross section which isperpendicular to the cell extending direction, the center portion 21 amay have a constant thickness (the whole center portion 21 a has thesame thickness), may become thicker toward the peripheral edge 21 bb, ormay have another “shape having a changing thickness in accordance withthe position”. When the center portion has the width in the peripheraldirection, the thickness of the center portion 21 a is preferably theconstant thickness (the whole center portion 21 a has the samethickness). When the thickness of the center portion 21 a increasestoward the peripheral edge 21 bb, the surface of the center portion 21 ais preferably a flat surface. When the surface of the center portion 21a is the flat surface, a member such as an electrode terminal protrudingportion is easily disposed. In the honeycomb structure 500 of thepresent embodiment, when the electrode section 21 is formed so as tobecome thinner gradually from the center point in the peripheraldirection toward both the ends in the cross section which isperpendicular to the cell extending direction, the center portion of theelectrode section 21 in the peripheral direction is the center point ofthe electrode section 21 in the peripheral direction. Moreover, when theelectrode section 21 has, for example, the constant thickness in apredetermined region (the width) including the center point in theperipheral direction in the cross section which is perpendicular to thecell extending direction, the center portion of the electrode section 21in the peripheral direction is in the region having the constantthickness (the width). In the honeycomb structure of the presentembodiment, when “the center portion in the peripheral direction (thecenter portion)” of the electrode section is “the portion positioned atthe center of the electrode section in the peripheral direction andhaving the width in the peripheral direction” in the cross section whichis perpendicular to the cell extending direction, the center point ofthe electrode section in the peripheral direction preferably coincideswith the center point of “the center portion” of the electrode sectionin the peripheral direction.

In the honeycomb structure 500 of the present embodiment, a thickness ofthe center portion 21 a of the electrode section 21 is preferably from0.2 to 5 mm, and further preferably from 0.5 to 3 mm. When the thicknessis smaller than 0.2 mm, the effect of decreasing the bias of thetemperature distribution when applying the voltage of the honeycombstructure deteriorates sometimes. When the thickness is larger than 5mm, the honeycomb structure is not easily inserted sometimes wheninserting the structure into a tubular can member.

In the honeycomb structure 500 of the present embodiment, an angle of0.5 time a central angle of the center portion 21 a of the electrodesection 21 is preferably 25° or smaller in the cross section which isperpendicular to the cell extending direction. When the angle is largerthan 25°, the effect of lowering a temperature around both the ends(both the peripheral edges) of the electrode section 21 of the honeycombstructure 500 deteriorates sometimes.

In the honeycomb structure 500 of the present embodiment, when thecenter point of the electrode section 21 in the peripheral direction(the peripheral direction of the honeycomb structure section) is aposition of “0°” and the peripheral edge 21 bb of the electrode section21 is a position of “an angle θ of 0.5 time a central angle α of theelectrode section 21” (the position of the angle θ) in the cross sectionwhich is perpendicular to the cell extending direction, a thickness ofthe electrode section 21 at a position of “0.5 time the angle θ (0.5θ)”(the position rotated as much as 0.5θ in the peripheral direction from“the position of 0°” toward “the position of the angle θ” (a midpointbetween “the position of 0°” and “the position of the angle θ”)) ispreferably 95% or smaller, further preferably from 10 to 90%, andespecially preferably from 15 to 85% of the thickness of the electrodesection 21 at the center point in the peripheral direction. When thethickness is larger than 95%, the effect of suppressing the bias of thetemperature distribution when applying the voltage to the honeycombstructure deteriorates sometimes.

Moreover, in the honeycomb structure 500 of the present embodiment, athickness of the electrode section 21 at a position of “0.8 time theangle θ (0.8θ)” is preferably 80% or smaller, further preferably from0.5 to 75%, and especially preferably from 1 to 65% of the thickness ofthe electrode section 21 at the center point in the peripheraldirection, in the cross section which is perpendicular to the cellextending direction. When the thickness is larger than 80%, the effectof suppressing the bias of the temperature distribution when applyingthe voltage to the honeycomb structure deteriorates sometimes.

The honeycomb structure 500 of the present embodiment further preferablysatisfies conditions of both the thickness of the electrode section atthe above “position of 0.5θ” and the thickness of the electrode sectionat the above “position of 0.8θ”.

In the honeycomb structure 500 of the present embodiment, the electricalresistivity of the electrode section 21 is preferably from 0.1 to 100Ωcm, further preferably from 0.5 to 20 Ωcm, especially preferably from 1to 3 Ωcm, and most preferably from 1 to 2 Ωcm. When the electricalresistivity is smaller than 0.1 Ωcm, the end portions of the electrodesection in the peripheral direction generate heat in a concentratedmanner sometimes. When the electrical resistivity is larger than 100 Ωm,the current does not easily flow sometimes, and the effect of generatingthe heat evenly in the honeycomb structure (decreasing the bias of thetemperature distribution) deteriorates sometimes.

In the honeycomb structure 500 of the present embodiment, the electrodesection 21 preferably contains silicon carbide particles and silicon asmain components, and is further preferably formed by using the siliconcarbide particles and silicon as raw materials except usually containedimpurities. Here, when “the silicon carbide particles and silicon areused as the main components”, it is meant that a total mass of thesilicon carbide particles and silicon is 90 mass % or larger than a massof the whole electrode section. Thus, when the electrode section 21contains the silicon carbide particles and silicon as the maincomponents, the component of the electrode section 21 is the same as orclose to a component of a honeycomb structure section 4 (when thematerial of the honeycomb structure section is silicon carbide), so thata thermal expansion coefficient of the electrode section 21 is the sameas or close to that of the honeycomb structure section 4. Moreover,since the materials are the same or close, a joining strength betweenthe electrode section 21 and the honeycomb structure section 4 alsoincreases. Therefore, even when heat stress is applied to the honeycombstructure, the electrode section 21 can be prevented from peeling fromthe honeycomb structure section 4, or a joined portion between theelectrode section 21 and the honeycomb structure section 4 can beprevented from being broken.

When the electrode section 21 contains the silicon carbide particles andsilicon as the main components, a ratio of a mass of silicon containedin the electrode section 21 to “the total of the masses of the siliconcarbide particles and silicon” contained in the electrode section 21 ispreferably from 20 to 40 mass %, and further preferably from 25 to 35mass %. In consequence, the electrical resistivity of the electrodesection 21 can be in a range of 0.1 to 100 Ωcm. When the ratio issmaller than 20 mass %, the electrical resistivity increases, a strengthto bind silicon carbide deteriorates, and the electrode section 21easily deteriorates sometimes.

When the main components of the electrode section 21 are the siliconcarbide particles and silicon, an average particle diameter of thesilicon carbide particles contained in the electrode section 21 ispreferably from 10 to 60 μm, and further preferably from 20 to 60 μm.When the average particle diameter of the silicon carbide particlescontained in the electrode section 21 is in such a range, the electricalresistivity of the electrode section 21 can be in a range of 0.1 to 100Ωcm. When an average pore diameter of the silicon carbide particlescontained in the electrode section 21 is smaller than 10 μm, theelectrical resistivity of the electrode section 21 excessively increasessometimes. When the average pore diameter of the silicon carbideparticles contained in the electrode section 21 is larger than 60 μm,the strength of the electrode section 21 decreases, and the sectioneasily breaks sometimes. The average particle diameter of the siliconcarbide particles contained in the electrode section 21 is a valuemeasured by a laser diffraction process.

A porosity of the electrode section 21 is preferably from 30 to 60%, andfurther preferably from 30 to 55%. When the porosity of the electrodesection 21 is in such a range, a suitable electrical resistivity can beobtained. When the porosity of the electrode section 21 is smaller than30%, the section is deformed sometimes during manufacturing. When theporosity is larger than 60%, the electrical resistivity excessivelyincreases sometimes. The porosity is the value measured by a mercuryporosimeter.

The average pore diameter of the electrode section 21 is preferably from5 to 45 μm, and further preferably from 7 to 40 μm. When the averagepore diameter of the electrode section 21 is in such a range, thesuitable electrical resistivity can be obtained. When the average porediameter of the electrode section 21 is smaller than 5 μm, theelectrical resistivity of the electrode section 21 excessively increasessometimes. When the average pore diameter is larger than 45 μm, thestrength of the electrode section 21 decreases, and the section easilybreaks sometimes. The average pore diameter is the value measured by amercury porosimeter.

Also in the honeycomb structure 500 of the present embodiment, theelectrode section 21 may be provided with an electrode terminalprotruding portion.

(2) Manufacturing Method of Honeycomb Structure:

Next, a manufacturing method of the honeycomb structure of the presentinvention will be described. There will be described a method ofmanufacturing the honeycomb structure 200 (see FIG. 4 to FIG. 6) whichis still another embodiment of the above honeycomb structure of thepresent invention.

First, metal silicon powder (metal silicon), a binder, a surfactant, apore former, water and the like are added to silicon carbide powder(silicon carbide), to prepare a forming raw material. A mass of metalsilicon is preferably from 10 to 40 mass % of a total of a mass of thesilicon carbide powder and the mass of metal silicon. An averageparticle diameter of the silicon carbide particles in the siliconcarbide powder is preferably from 3 to 50 μm, and further preferablyfrom 3 to 40 μm. An average particle diameter of metal silicon (themetal silicon powder) is preferably from 2 to 35 μm. The averageparticle diameters of the silicon carbide particles and metal silicon(the metal silicon particles) are values measured by the laserdiffraction process. The silicon carbide particles are fine particles ofsilicon carbide constituting the silicon carbide powder. The metal,silicon particles are fine particles of metal silicon constituting themetal silicon powder. Additionally, this is a blend of the forming rawmaterials when the material of the honeycomb structure section is thesilicon-silicon carbide composite material, and metal silicon is notadded when the material of the honeycomb structure section is siliconcarbide.

Examples of the binder can include methylcellulose, hydroxypropylmethylcellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose,carboxymethylcellulose, and polyvinyl alcohol. Among these binders,methylcellulose and hydroxypropoxyl cellulose are preferably usedtogether. A content of the binder is preferably from 2.0 to 10.0 partsby mass while the total mass of the silicon carbide powder and the metalsilicon powder is 100 parts by mass.

A content of the water is preferably from 20 to 60 parts by mass whilethe total mass of the silicon carbide powder and the metal siliconpowder is 100 parts by mass.

As the surfactant, ethylene glycol, dextrin, fatty acid soap,polyalcohol or the like can be used. These surfactants may be usedalone, or two or more of the surfactants may be combined and used. Acontent of the surfactant is preferably from 0.1 to 2.0 parts by masswhile the total mass of the silicon carbide powder and the metal siliconpowder is 100 parts by mass.

There is not any special restriction on the pore former as long as poresare formed after firing, and examples of the pore former can includegraphite, starch, a resin balloon, a water absorbing resin, and silicagel. A content of the pore former is preferably from 0.5 to 10.0 partsby mass while the total mass of the silicon carbide powder and the metalsilicon powder is 100 parts by mass. An average particle diameter of thepore former is preferably from 10 to 30 μm. When the average particlediameter is smaller than 10 μm, the pores cannot sufficiently be formedsometimes. When the average particle diameter is larger than 30 μm, adie is clogged during forming. The average particle diameter of the poreformer is the value measured by the laser diffraction process.

Next, the forming raw materials are kneaded to form a kneaded material.There is not any special restriction on a method of kneading the formingraw materials to form the kneaded material, and examples of the methodcan include methods using a kneader, a vacuum clay kneader and the like.

Next, the kneaded material is extruded, to form a honeycomb formed body.During the extrusion forming, a die having a desirable entire shape,cell shape, partition wall thickness, cell density and the like ispreferably used. As a material of the die, a hard metal which does noteasily wear is preferable. The honeycomb formed body has a constitutionincluding partition walls to partition and form a plurality of cellswhich become through channels of a fluid, and an outer peripheral wallpositioned in an outermost periphery.

The partition wall thickness, the cell density, the outer peripheralwall thickness and the like of the honeycomb formed body can suitably bedetermined in accordance with a constitution of the honeycomb structureof the present invention to be prepared, in consideration of contractionduring drying and firing.

The obtained honeycomb formed body is preferably dried. There is not anyspecial restriction on a drying method, and examples of the dryingmethod can include electromagnetic wave heating systems such asmicrowave heating drying and high frequency dielectric heating drying,and external heating systems such as hot air drying and superheatingwater vapor drying. Among these methods, a method of drying apredetermined amount of a water content by the electromagnetic waveheating system, and then drying the remaining water content by theexternal heating system is preferable in that the whole formed body canquickly and evenly dried so as to prevent cracks from being generated.As drying conditions, the water content of 30 to 99 mass % of the watercontent prior to the drying is preferably removed by the electromagneticwave heating system, and then the water content is preferably decreasedto 3 mass % or smaller by the external heating system. As theelectromagnetic wave heating system, the dielectric heating drying ispreferable, and as the external heating system, the hot air drying ispreferable.

When a length of the honeycomb formed body in a central axis directionis not a desirable length, both end surfaces (both the end portions) arepreferably cut to obtain the desirable length. There is not any specialrestriction on a cutting method, but examples of the method can includea method using a disc saw cutter or the like.

Next, a center portion forming raw material to form the center portionof each electrode section is prepared. When the main components of thecenter portion are silicon carbide and silicon, the center portionforming raw material is preferably formed by adding predeterminedadditives to the silicon carbide powder and silicon powder, and kneadingthe materials.

Specifically, metal silicon powder (metal silicon), a binder, asurfactant, a pore former, water and the like are added to siliconcarbide powder (silicon carbide), to knead and prepare the centerportion forming raw material. A mass of metal silicon is preferably from20 to 50 parts by mass while a total mass of the silicon carbide powderand metal silicon is 100 parts by mass. An average particle diameter ofthe silicon carbide particles in the silicon carbide powder ispreferably from 10 to 60 μm. When the average particle diameter islarger than 60 μm, the electrical resistivity excessively increasessometimes. An average particle diameter of the metal silicon powder(metal silicon) is preferably from 2 to 20 μm. When the average particlediameter is larger than 20 μm, the electrical resistivity excessivelyincreases sometimes. The average particle diameters of the siliconcarbide particles and metal silicon (the metal silicon particles) arevalues measured by the laser diffraction process. The silicon carbideparticles are fine particles of silicon carbide constituting the siliconcarbide powder, and the metal silicon particles are fine particles ofmetal silicon constituting the metal silicon powder.

Examples of the binder can include methylcellulose, hydroxypropylmethylcellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose,carboxymethylcellulose, and polyvinyl alcohol. Among these binders,methylcellulose and hydroxypropoxyl cellulose are preferably usedtogether. A content of the binder is preferably from 0.1 to 5.0 parts bymass while the total mass of the silicon carbide powder and the metalsilicon powder is 100 parts by mass.

A content of the water is preferably from 15 to 60 parts by mass whilethe total mass of the silicon carbide powder and the metal siliconpowder is 100 parts by mass.

As the surfactant, ethylene glycol, dextrin, fatty acid soap,polyalcohol or the like can be used. These surfactants may be usedalone, or two or more of the surfactants may be combined and used. Acontent of the surfactant is preferably from 0.1 to 2.0 parts by masswhile the total mass of the silicon carbide powder and the metal siliconpowder is 100 parts by mass.

There is not any special restriction on the pore former as long as thepores are formed after the firing, and examples of the pore former caninclude graphite, starch, a resin balloon, a water absorbing resin, andsilica gel. A content of the pore former is preferably from 0.1 to 5.0parts by mass while the total mass of the silicon carbide powder and themetal silicon powder is 100 parts by mass. An average particle diameterof the pore former is preferably from 10 to 30 μm. When the averageparticle diameter is smaller than 10 μm, the pores cannot sufficientlybe formed sometimes. When the average particle diameter is larger than30 μm, large pores are easily formed, and strength deterioration occurssometimes. The average particle diameter of the pore former is the valuemeasured by the laser diffraction process.

Then, a mixture obtained by mixing the silicon carbide powder (siliconcarbide), metal silicon (the metal silicon powder), the binder, thesurfactant, the pore former, the water and the like is preferablykneaded to prepare the paste-like center portion forming raw material.There is not any special restriction on a kneading method and, forexample, a vertical stirrer can be used.

Next, an expanded portion forming raw material to form each of theexpanded portions of each of the electrode sections is prepared. Whenthe main components of the expanded portion are silicon carbide andsilicon, the expanded portion forming raw material is preferably formedby adding predetermined additives to silicon carbide powder and siliconpowder and kneading the materials.

Specifically, metal silicon powder (metal silicon), a binder, asurfactant, a pore former, water and the like are added to siliconcarbide powder (silicon carbide), to knead and prepare the expandedportion forming raw material. A mass of metal silicon is preferably from20 to 40 parts by mass while a total mass of the silicon carbide powderand metal silicon is 100 parts by mass. An average particle diameter ofthe silicon carbide particles in the silicon carbide powder ispreferably from 10 to 60 μm. When the average particle diameter islarger than 60 μm, the electrical resistivity excessively increasessometimes. An average particle diameter of the metal silicon powder(metal silicon) is preferably from 2 to 20 μm. When the average particlediameter is larger than 20 μm, the electrical resistivity excessivelyincreases sometimes. The average particle diameters of the siliconcarbide particles and metal silicon (the metal silicon particles) arethe values measured by the laser diffraction process. The siliconcarbide particles are fine particles of silicon carbide constituting thesilicon carbide powder, and the metal silicon particles are fineparticles of metal silicon constituting the metal silicon powder.

Examples of the binder can include methylcellulose, hydroxypropylmethylcellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose,carboxymethylcellulose, and polyvinyl alcohol. Among these binders,methylcellulose and hydroxypropoxyl cellulose are preferably usedtogether. A content of the binder is preferably from 0.1 to 5.0 parts bymass while the total mass of the silicon carbide powder and the metalsilicon powder is 100 parts by mass.

A content of the water is preferably from 15 to 60 parts by mass whilethe total mass of the silicon carbide powder and the metal siliconpowder is 100 parts by mass.

As the surfactant, ethylene glycol, dextrin, fatty acid soap,polyalcohol or the like can be used. These surfactants may be usedalone, or two or more of the surfactants may be combined and used. Acontent of the surfactant is preferably from 0.1 to 2.0 parts by masswhile the total mass of the silicon carbide powder and the metal siliconpowder is 100 parts by mass.

There is not any special restriction on the pore former as long as thepores are formed after the firing, and examples of the pore former caninclude graphite, starch, a resin balloon, a water absorbing resin, andsilica gel. A content of the pore former is preferably from 0.1 to 5.0parts by mass while the total mass of the silicon carbide powder and themetal silicon powder is 100 parts by mass. An average particle diameterof the pore former is preferably from 10 to 30 μm. When the averageparticle diameter is smaller than 10 μm, the pores cannot sufficientlybe formed sometimes. When the average particle diameter is larger than30 μm, large pores are easily formed, and strength deterioration occurssometimes. The average particle diameter of the pore former is the valuemeasured by the laser diffraction process.

Next, a mixture obtained by mixing the silicon carbide powder (siliconcarbide), metal silicon (the metal silicon powder), the binder, thesurfactant, the pore former, the water and the like is preferablykneaded to prepare the paste-like expanded portion forming raw material.There is not any special restriction on a kneading method and, forexample, the vertical stirrer can be used.

Next, the side surface of the dried honeycomb formed body is preferablycoated with the obtained center portion forming raw material andexpanded portion forming raw material, respectively, to obtain shapes ofthe center portion 21 a and the expanded portion 21 b of the electrodesection 21 in the honeycomb structure 200 shown in FIG. 4 to FIG. 6.There is not any special restriction on a method of coating the sidesurface of the honeycomb formed body with the center portion forming rawmaterial and expanded portion forming raw material, but, for example, aprinting method can be used. Thicknesses of the center portion and theexpanded portion of the electrode section can be desirable thicknessesby regulating the thicknesses of the center portion forming raw materialand the expanded portion forming raw material at the coating. Thus, whenthe side surface of the honeycomb formed body is simply coated with thecenter portion forming raw material and expanded portion forming rawmaterial, dried and fired, the center portion and the expanded portionof the electrode section can be formed, and hence the electrode sectioncan very easily be formed.

Additionally, when the honeycomb structure “where each electrode sectiondoes not have any boundary portions and is continuously formed in thecross section which is perpendicular to the cell extending direction”(see FIG. 10 to FIG. 12) is prepared, similarly to the above expandedportion forming raw material, a raw material to form the electrodesection (the electrode section forming raw material) is prepared, andthe side surface of the dried honeycomb formed body is preferably coatedwith the obtained electrode section forming raw material so as to obtaina shape of the electrode section 21 in the honeycomb structure 500 shownin FIG. 10 to FIG. 12.

Next, the center portion forming raw material and the expanded portionforming raw material which coat the side surface of the honeycomb formedbody are preferably dried. Drying conditions are preferably from 50 to100° C.

Next, an electrode terminal protruding portion forming member ispreferably prepared. The electrode terminal protruding portion formingmember is attached to the honeycomb formed body to form the electrodeterminal protruding portion. There is not any special restriction on ashape of the electrode terminal protruding portion forming member, butthe member is preferably formed into a shape shown in, for example, FIG.4 to FIG. 6. Then, the obtained electrode terminal protruding portionforming member is preferably attached to a portion coated with thecenter portion forming raw material in the honeycomb formed body coatedwith the center portion forming raw material. Additionally, an order ofthe preparation of the honeycomb formed body, the preparation of thecenter portion forming raw material, the preparation of the expandedportion forming raw material and the preparation of the electrodeterminal protruding portion forming member may be any order.

The electrode terminal protruding portion forming member is preferablyobtained by forming and drying a electrode terminal protruding portionforming raw material (the raw material to form the electrode terminalprotruding portion forming member). When main components of theelectrode terminal protruding portion are silicon carbide and silicon,the electrode terminal protruding portion forming raw material ispreferably formed by adding predetermined additives to the siliconcarbide powder and silicon powder, and kneading the materials.

Specifically, metal silicon powder (metal silicon), a binder, asurfactant, a pore former, water and the like are added to siliconcarbide powder (silicon carbide), to knead and prepare the electrodeterminal protruding portion forming raw material. A mass of metalsilicon is preferably from 20 to 40 mass % of a total of masses of thesilicon carbide powder and metal silicon. An average particle diameterof the silicon carbide particles in the silicon carbide powder ispreferably from 10 to 60 μm. When the average particle diameter issmaller than 10 μm, the electrical resistivity excessively decreasessometimes. When the average particle diameter is larger than 60 μm, theelectrical resistivity excessively increases sometimes. An averageparticle diameter of the metal silicon powder (metal silicon) ispreferably from 2 to 20 μm. When the average particle diameter issmaller than 2 μm, the electrical resistivity excessively decreasessometimes. When the average particle diameter is larger than 20 μm, theelectrical resistivity excessively increases sometimes. The averageparticle diameters of the silicon carbide particles and metal siliconparticles (metal silicon) are values measured by the laser diffractionprocess. The silicon carbide particles are fine particles of siliconcarbide constituting the silicon carbide powder, and the metal siliconparticles are fine particles of metal silicon constituting the metalsilicon powder.

Examples of the binder can include methylcellulose, hydroxypropylmethylcellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose,carboxymethylcellulose, and polyvinyl alcohol. Among these binders,methylcellulose and hydroxypropoxyl cellulose are preferably usedtogether. A content of the binder is preferably from 2.0 to 10.0 partsby mass while the total mass of the silicon carbide powder and the metalsilicon powder is 100 parts by mass.

A content of the water is preferably from 20 to 40 parts by mass whilethe total mass of the silicon carbide powder and the metal siliconpowder is 100 parts by mass.

As the surfactant, ethylene glycol, dextrin, fatty acid soap,polyalcohol or the like can be used. These surfactants may be usedalone, or two or more of the surfactants may be combined and used. Acontent of the surfactant is preferably from 0.1 to 2.0 parts by masswhile the total mass of the silicon carbide powder and the metal siliconpowder is 100 parts by mass.

There is not any special restriction on the pore former as long as thepores are formed after the firing, and examples of the pore former caninclude graphite, starch, a resin balloon, a water absorbing resin, andsilica gel. A content of the pore former is preferably from 0.1 to 5.0parts by mass while the total mass of the silicon carbide powder and themetal silicon powder is 100 parts by mass. An average particle diameterof the pore former is preferably from 10 to 30 μm. When the averageparticle diameter is smaller than 10 μm, the pores cannot sufficientlybe formed sometimes. When the average particle diameter is larger than30 μm, the die is clogged at the forming. The average particle diameterof the pore former is the value measured by the laser diffractionprocess.

Next, a mixture obtained by mixing the silicon carbide powder (siliconcarbide), metal silicon (the metal silicon powder), the binder, thesurfactant, the pore former, the water and the like is preferablykneaded to form the electrode terminal protruding portion forming rawmaterial. There is not any special restriction on a kneading method and,for example, the vertical stirrer can be used.

There is not any special restriction on a method of forming the obtainedelectrode terminal protruding portion forming raw material into theshape of the electrode terminal protruding portion forming member, andexamples of the method can include a method of processing the memberafter extrusion forming.

The electrode terminal protruding portion forming raw material ispreferably formed into the shape of the electrode terminal protrudingportion forming member, and then dried to obtain the electrode terminalprotruding portion forming member. Drying conditions are preferably from50 to 100° C.

Next, the electrode terminal protruding portion forming member ispreferably attached to the honeycomb formed body coated with the centerportion forming raw material. There is not any special restriction on amethod of attaching the electrode terminal protruding portion formingmember to the honeycomb formed body (the portion of the honeycomb formedbody which is coated with the center portion forming raw material), butthe electrode terminal protruding portion forming member is preferablyattached to the honeycomb formed body by use of the above center portionforming raw material. For example, “the surface of the electrodeterminal protruding portion forming member which is attached to thehoneycomb formed body (the surface which comes in contact with thehoneycomb formed body)” is preferably coated with the center portionforming raw material, and the electrode terminal protruding portionforming member is preferably attached to the honeycomb formed body sothat “the surface coated with the center portion forming raw material”comes in contact with the honeycomb formed body.

Then, “the honeycomb formed body which is coated with the center portionforming raw material and the expanded portion forming raw material andto which the electrode terminal protruding portion forming member isattached” is preferably dried and fired, to obtain the honeycombstructure of the present invention.

Drying conditions at this time are preferably from 50 to 100° C.

Moreover, calcinating is preferably performed to remove the binder andthe like prior to the firing. The calcinating is preferably performed at400 to 5000° C. in the atmosphere for 0.5 to 20 hours. There is not anyspecial restriction on a calcinating and firing method, and the firingcan be performed by using an electric furnace, a gas furnace or thelike. As firing conditions, heating is preferably performed at 1400 to1500° C. in an inactive atmosphere of nitrogen, argon or the like for 1to 20 hours. Moreover, an oxidation treatment is preferably performed at1200 to 1350° C. for 1 to 10 hours after the firing, to enhancedurability.

It is to be noted that the electrode terminal protruding portion formingmember may be attached before firing the honeycomb formed body, orattached after firing the honeycomb formed body. When the electrodeterminal protruding portion forming member is attached to the honeycombformed body after the firing, the member is preferably fired again onthe above conditions afterwards.

EXAMPLES

Hereinafter, the present invention will further specifically bedescribed with respect to examples, but the present invention is notlimited to theses examples.

Example 1

Silicon carbide (SiC) powder and metal silicon (Si) powder were mixed ata mass rate of 80:20, hydroxypropyl methylcellulose as a binder and awater absorbing resin as a pore former were added to this mixture, waterwas also added to obtain a forming raw material, and the forming rawmaterial was kneaded by a vacuum clay kneader, to prepare a columnarkneaded material. A content of the binder was 7 parts by mass while atotal of the silicon carbide (SiC) powder and the metal silicon (Si)powder was 100 parts by mass, a content of the pore former was 3 partsby mass while the total of the silicon carbide (SiC) powder and themetal silicon (Si) powder was 100 parts by mass, and a content of thewater was 42 parts by mass while the total of the silicon carbide (SiC)powder and the metal silicon (Si) powder was 100 parts by mass. Anaverage particle diameter of the silicon carbide powder was 20 μm, andan average particle diameter of the metal silicon powder was 6 μm.Moreover, an average particle diameter of the pore former was 20 μm. Theaverage particle diameters of silicon carbide, metal silicon and thepore former were values measured by a laser diffraction process.

The obtained columnar kneaded material was formed by using an extrusionforming machine, to obtain a honeycomb formed body. The obtainedhoneycomb formed body was dried by high frequency dielectric heating,dried at 120° C. for two hours by use of a hot air drier, and then bothend surfaces of the formed body were cut as much as a predeterminedamount.

Next, a center portion forming raw material was prepared. First, siliconcarbide (SiC) powder and metal silicon (Si) powder were mixed at a massrate of 60:40, to this mixture, there were added hydroxypropylmethylcellulose as a binder, glycerin as a moisture retaining agent, anda surfactant as a dispersing agent, and water was also added to mix thematerials. The mixture was kneaded to obtain the center portion formingraw material. A content of the binder was 0.5 part by mass while a totalof the silicon carbide (SiC) powder and the metal silicon (Si) powderwas 100 parts by mass, a content of glycerin was 10 parts by mass whilethe total of the silicon carbide (SiC) powder and the metal silicon (Si)powder was 100 parts by mass, a content of the surfactant was 0.3 partby mass while the total of the silicon carbide (SiC) powder and themetal silicon (Si) powder was 100 parts by mass, and a content of thewater was 42 parts by mass while the total of the silicon carbide (SiC)powder and the metal silicon (Si) powder was 100 parts by mass. Anaverage particle diameter of the silicon carbide powder was 52 μm, andan average particle diameter of the metal silicon powder was 6 μm. Theaverage particle diameters of silicon carbide and metal silicon werevalues measured by the laser diffraction process. The kneading wasperformed by a vertical stirrer.

Next, an expanded portion forming raw material was prepared. First,silicon carbide (SiC) powder and metal silicon (Si) powder were mixed ata mass rate (SiC:Si) of 70:30, to this mixture, there were addedhydroxypropyl methylcellulose as a binder, glycerin as a moistureretaining agent, and a surfactant as a dispersing agent, and water wasalso added to mix the materials. The mixture was kneaded to obtain theexpanded portion forming raw material. A content of the binder was 0.5part by mass while the total of the silicon carbide (SiC) powder and themetal silicon (Si) powder was 100 parts by mass, a content of glycerinwas 10 parts by mass while the total of the silicon carbide (SiC) powderand the metal silicon (Si) powder was 100 parts by mass, a content ofthe surfactant was 0.3 part by mass while the total of the siliconcarbide (SiC) powder and the metal silicon (Si) powder was 100 parts bymass, and a content of the water was 42 parts by mass while the total ofthe silicon carbide (SiC) powder and the metal silicon (Si) powder was100 parts by mass. An average particle diameter of the silicon carbidepowder was 52 μm, and an average particle diameter of the metal siliconpowder was 6 μm. The average particle diameters of silicon carbide andmetal silicon were values measured by the laser diffraction process. Thekneading was performed by the vertical stirrer.

Next, the side surface of the dried honeycomb formed body was coatedwith the center portion forming raw material and the expanded portionforming raw material in such a band-like shape as to extend over boththe end surfaces of the honeycomb formed body, so that shapes of thecenter portion 21 a and the expanded portion 21 b of the electrodesection 21 of the honeycomb structure 200 shown in FIG. 4 to FIG. 6 wereformed.

Next, the center portion forming raw material and the expanded portionforming raw material which coated the honeycomb formed body were dried.Drying condition was 70° C.

Next, an electrode terminal protruding portion forming member wasprepared. First, silicon carbide (SiC) powder and metal silicon (Si)powder were mixed at a mass rate of 60:40, hydroxypropyl methylcelluloseas a binder was added to this mixture, and water was also added to mixthe materials. The mixture was kneaded to obtain an electrode terminalprotruding portion forming raw material. The electrode terminalprotruding portion forming raw material was kneaded by using a vacuumclay kneader to obtain a kneaded material. A content of the binder was 4parts by mass while the total of the silicon carbide (SiC) powder andthe metal silicon (Si) powder was 100 parts by mass, and a content ofwater was 22 parts by mass while the total of the silicon carbide (SiC)powder and the metal silicon (Si) powder was 100 parts by mass. Anaverage particle diameter of the silicon carbide powder was 52 μm, andan average particle diameter of the metal silicon powder was 6 μm. Theaverage particle diameters of silicon carbide and metal silicon werevalues measured by the laser diffraction process.

The obtained kneaded material was formed by using the vacuum claykneader, processed into a shape of the electrode terminal protrudingportion 22 shown in FIG. 4 to FIG. 6 (the shape including a substrateand a protruding portion), and dried, to obtain the electrode protrudingforming member. Moreover, drying condition was 70° C. A portioncorresponding to the plate-like substrate 22 a had a size of “3 mm×1.2mm×15 mm”. Furthermore, a portion corresponding to the protrudingportion 22 b was formed into a columnar shape having a bottom surfacediameter of 7 mm and a length of 10 mm in a central axis direction. Twoelectrode terminal protruding portion forming members were prepared.

Next, the two electrode terminal protruding portion forming members wereattached to two portions of the honeycomb formed body which were coatedwith the center portion forming raw material, respectively. Theelectrode terminal protruding portion forming members were attached tothe portion of the honeycomb formed body which was coated with thecenter portion forming raw material, by use of the center portionforming raw material. Afterward, “the honeycomb formed body which wascoated with the center portion forming raw material and the expandedportion forming raw material and to which the electrode terminalprotruding portion forming members were attached” was degreased, fired,and further subjected to an oxidation treatment to obtain a honeycombstructure. Degreasing conditions were 550° C. for three hours. Firingconditions were 1450° C. in an argon atmosphere for two hours. Oxidationtreatment conditions were 1300° C. for one hour.

An average pore diameter (pore diameters) of partition walls of theobtained honeycomb structure was 8.6 μm, and a porosity thereof was 41%.The average pore diameter and the porosity were values measured by amercury porosimeter. Moreover, in the honeycomb structure, a partitionwall thickness was 109 μm, and a cell density was 93 cells/cm². Inaddition, the bottom surface of the honeycomb structure had a roundshape with a diameter of 93 mm, and a length of the honeycomb structurein a cell extending direction was 100 mm. Moreover, an isostaticstrength of the obtained honeycomb structure was 2.5 MPa. The isostaticstrength was a breaking strength measured under a hydrostatic pressurein water.

Moreover, an angle of 0.5 time a central angle of the electrode section(the whole electrode section) in a cross section of the honeycombstructure which was perpendicular to the cell extending direction was40°. Moreover, a thickness of the center portion of the electrodesection was 3.0 mm, and a length of the center portion in a peripheraldirection in the cross section which was perpendicular to the cellextending direction was 20 mm (an angle θ of 0.5 time a central angle αwas about 12.4°). Furthermore, an electrical resistivity of the centerportion of the electrode section was 0.6 Ωcm, an electrical resistivityof the expanded portion of the electrode section was 1.3 Ωcm, anelectrical resistivity of a honeycomb structure section was 48 Ωcm, andan electrical resistivity of the electrode terminal protruding portionwas 1.3 Ωcm. Moreover, one of the two electrode sections in the crosssection which was perpendicular to the cell extending direction wasdisposed on an opposite side of the other electrode section via thecenter of the honeycomb formed body. Moreover, a thickness of the centerportion of the electrode section was 3 mm, and was an even thickness.Furthermore, when the center point of the electrode section in theperipheral direction was a position of “0°” and the peripheral edge ofthe electrode section was a position of “the angle θ of 0.5 time thecentral angle α of the electrode section” in the cross section which wasperpendicular to the cell extending direction, a thickness of theelectrode section 21 at a position of “0.5 time the angle θ (0.5θ)” was75% of the thickness of the electrode section at the center point in theperipheral direction. Additionally, in the cross section which wasperpendicular to the cell extending direction, a thickness of theelectrode section at a position of “0.8 time the angle θ (0.8θ)” was 25%of the thickness of the electrode section at the center point in theperipheral direction.

There was measured a temperature (the highest temperature) at a positionP (see FIG. 5) which came into contact with a side edge of the expandedportion of the electrode section, in the cross section which wasperpendicular to the cell extending direction, when applying a voltageof 600 V to the obtained honeycomb structure. The position which comesin contact with the side edge of the expanded portion of the electrodesection in the honeycomb structure section is a position through which acurrent flows most, and is a portion having the highest temperature inthe honeycomb structure. Results are shown in Table 1.

Additionally, the electrical resistivities of the honeycomb structuresection, the electrode section (the center portion and the expandedportion) and the electrode terminal protruding portion were measured bythe following method. A test piece of 10 mm×10 mm×50 mm was prepared byusing the same material as that of a measurement object (i.e., the testpieces were prepared by using the same material as that of the honeycombstructure section when measuring the electrical resistivity of thehoneycomb structure section, using the same material as that of theelectrode section when measuring the electrical resistivity of theelectrode section, and using the same material as that of the electrodeterminal protruding portion when measuring the electrical resistivity ofthe electrode terminal protruding portion, respectively). The wholesurfaces of both end portions of each test piece (the surface of 10mm×10 mm) were coated with a silver paste, and connected to an electricwiring so that energization was possible. The test piece was connectedto a voltage applying current measuring device, to apply the voltage. Athermocouple was disposed at the center portion of the test piece, and achange of a test piece temperature at the applying of the voltage withelapse of time was confirmed with a recorder. Six hundred V was applied,a current value and a voltage value in a state where the test piecetemperature was 400° C. were measured, and the electrical resistivitywas calculated from the obtained current value and voltage value and atest piece dimension.

TABLE 1 Electrical Electrode section resistivity of 0.5 time Electricalresistivity honeycomb central (Ωcm) structure Highest angle CenterExpanded section temp. (°) Whole portion portion Shape (Ωcm) (° C.)Example 1 40 — 0.6 1.3 With boundary 48 270 Example 2 23 — 0.6 1.3Boundary, 48 278 stepwise Comparative 40 0.1 or — — Constant 48 415Example 1 smaller thickness Comparative 40 0.6 — — Constant 48 355Example 2 thickness Comparative 40 1.3 — — Constant 48 320 Example 3thickness Comparative 10 1.3 — — Continuous 48 318 Example 4 Example 315 1.3 — — Continuous 48 284 Example 4 40 1.3 — — Continuous 48 280Example 5 65 1.3 — — Continuous 48 285 Comparative 70 1.3 — — Continuous48 320 Example 5 Comparative 40 1.3 — — Continuous 0.5 345 Example 6Example 6 40 1.3 — — Continuous 1 290 Example 7 40 1.3 — — Continuous200 288 Comparative 40 1.3 — — Continuous 210 322 Example 7

Example 2

A honeycomb structure was prepared similarly to Example 1, except thatthe thicknesses of two electrode section expanded portions of thehoneycomb structure were changed stepwise as shown in FIG. 7. Thethickness of the expanded portion was changed in three divided stages(regions A, B and C: see FIG. 7). The thickness of the region A whichcame in contact with a center portion was 3.0 mm, the thickness of theregion B which came in contact with the region A was 1.5 mm, and thethickness of the region C which came in contact with the region B andwas positioned on the outermost side was 0.5 mm. Moreover, in a crosssection which was perpendicular to a cell extending direction, a lengthof each of the regions A positioned on both sides of the center portionin a peripheral direction was 3 mm (a central angle was about 3.7°).Furthermore, in the cross section which was perpendicular to the cellextending direction, a length of each of the regions B positioned onouter sides of the regions A (on the opposite sides of a position of thecenter portion) in the peripheral direction was 12 mm (a central anglewas about 15.0°). Additionally, in the cross section which wasperpendicular to the cell extending direction, a length of each of theregions C positioned on outer sides of the regions B (on the oppositeside of the position of each of the regions A) in the peripheraldirection was 5 mm (a central angle was about 6.2°). Similarly toExample 1, “the highest temperature” of the honeycomb structure wasmeasured. Results are shown in Table 1. In Table 1, a column of “0.5time (°) the central angle” of “the electrode section” shows an angle of0.5 time the central angle of the electrode section in the cross sectionwhich is perpendicular to the cell extending direction. Moreover; in acolumn of “the shape” of “the electrode section”, “with the boundary” isdescribed, when the electrode section includes “the center portion” and“the expanded portion”, and the thickness of “the expanded portion”continuously changes (Example 1). Additionally, in the column of “theshape” of “the electrode section”, “boundary, stepwise” is described,when the electrode section includes “the center portion” and “theexpanded portion”, and the thickness of “the expanded portion” changesintermittently (stepwise) (Example 2).

Comparative Examples 1 to 3

Similarly to Example 1, honeycomb structures were prepared, except thateach electrode section was not divided into a center portion andexpanded portions, the whole electrode section had the same electricalresistivity, the whole electrode section had the same thickness (3 mm),and an electrical resistivity of the electrode section was changed asshown in Table 1 (Comparative Examples 1 to 3). Similarly to Example 1,“the highest temperature” of the honeycomb structure was measured.Results are shown in Table 1. In Table 1, a column of “whole” of “theelectrical resistivity (Ωcm)” of “the electrode section” shows theelectrical resistivities of the electrode sections of ComparativeExamples 1 to 3. Moreover, in the column of “the shape” of “theelectrode section”, “constant thickness” is described, when theelectrode section “does not have any boundary portions and arecontinuously formed in the cross section which is perpendicular to thecell extending direction” and the thickness of the electrode section iseven.

In Comparative Example 1, a material of the electrode section was acommercially available silver (Ag) paste which was hardened. Moreover,the electrode section was formed by coating a honeycomb formed body withthe silver (Ag) paste and hardening the paste.

In Comparative Example 2, a material of the electrode section was asilicon-silicon carbide composite material. The electrode section wasformed by coating a honeycomb formed body with the center portionforming raw material of Example 1 in which “a mass rate between siliconcarbide (SiC) powder and metal silicon (Si) powder” was “60:40”, andsintering the honeycomb formed body.

In Comparative Example 3, a material of the electrode section was asilicon-silicon carbide composite material. The electrode section wasformed by coating a honeycomb formed body with the center portionforming raw material of Example 1 in which “a mass rate (SiC:Si) betweensilicon carbide (SiC) powder and metal silicon (Si) powder” was “70:30”,and sintering the honeycomb formed body.

It is seen from Table 1 that in the honeycomb structures of Examples 1and 2, the electrical resistivity of the center portion of the electrodesection is smaller than the electrical resistivity of the expandedportion of the electrode section, each of the expanded portions isformed so as to become thinner from the end portion which comes incontact with the center portion toward the side edge which is theopposite end portion in the cross section which is perpendicular to thecell extending direction, and hence the highest temperature of thehoneycomb structure lowers. When the highest temperature of thehoneycomb structure lowers, it is indicated that the bias of thetemperature distribution in the honeycomb structure is suppressed.

Examples 3 to 7 and Comparative Examples 4 to 7

Honeycomb structures were prepared similarly to Example 1, except thatan electrode section was formed by using an expanded portion forming rawmaterial “so that the section did not have any boundary portions andwere continuously formed in a cross section which was perpendicular to acell extending direction”, and characteristics of the electrode sectionand an electrical resistivity of a honeycomb structure section werechanged as shown in Table 1 (Examples 3 to 7 and Comparative Examples 4to 7). The whole shape of the electrode section was formed so as to bethe same as the whole shape of the electrode section in Example 1 (theshape formed by combining a center portion and expanded portions).Similarly to Example 1, “the highest temperature” of the honeycombstructure was measured. Results are shown in Table 1. In Table 1, in acolumn of “the shape” of “the electrode section”, “continuously” isdescribed, when the electrode section “does not have any boundaryportions and is continuously formed in the cross section which isperpendicular to the cell extending direction”.

It is seen from Table 1 that when an angle of 0.5 time a central angleof the electrode section is from 15 to 65°, “the highest temperature”can be lowered. Moreover, it is seen that when “the electricalresistivity of the honeycomb structure section” is from 1 to 200 Ωcm,“the highest temperature” can be lowered.

INDUSTRIAL APPLICABILITY

A honeycomb structure of the present invention can suitably be used as acatalyst carrier for an exhaust gas purification device which purifiesan exhaust gas of a car.

DESCRIPTION OF REFERENCE NUMERALS

1: partition wall, 2: cell, 3: outer peripheral wall, 4: honeycombstructure section, 5: side surface, 11: one end surface, 12: other endsurface, 21: electrode section, 21 a: center portion, 21 b: expandedportion, 21 ba: end portion which comes in contact with the centerportion, 21 bb: peripheral edge (side edge), 21 c: one end portion of(the electrode section), 21 d: other end portion (of the electrodesection), 22: electrode terminal protruding portion, 22 a: substrate, 22b: protruding portion, 100, 200, 300, 400 and 500: honeycomb structure,O: center, α: central angle, β: angle, θ: angle of 0.5 time the centralangle, A, B, and C: region of the expanded portion of the electrodesection, P: position where the side edge of the expanded portion of theelectrode section comes in contact, and S: portion which becomes aboundary (the boundary surface).

The invention claimed is:
 1. A honeycomb structure comprising: a tubularhoneycomb structure section including porous partition walls whichpartition and form a plurality of cells extending from one end surfaceto the other end surface to become through channels of a fluid, and anouter peripheral wall positioned in an outermost periphery; and a pairof electrode sections arranged on a side surface of the honeycombstructure section, wherein an electrical resistivity of the honeycombstructure section is from 1 to 200 Ωcm, each of the pair of electrodesections is formed into a band-like shape extending in a cell extendingdirection of the honeycomb structure section, the one electrode sectionin the pair of electrode sections is disposed on an opposite side of theother electrode section in the pair of electrode sections via the centerof the honeycomb structure section in a cross section which isperpendicular to the cell extending direction, an angle which is 0.5times as large as a central angle of each of the electrode sections isfrom 15 to 65° in the cross section which is perpendicular to the cellextending direction, and each of the electrode sections is formed so asto become thinner from a center portion in a peripheral direction towardboth ends in the peripheral direction in the cross section which isperpendicular to the cell extending direction.
 2. The honeycombstructure according to claim 1, wherein each of the electrode sectionsis constituted of the center portion in the peripheral direction, andexpanded portions positioned on both sides of the center portion in theperipheral direction in the cross section which is perpendicular to thecell extending direction, and the electrical resistivity of the centerportion of the electrode section is smaller than that of each of theexpanded portions of the electrode section.
 3. The honeycomb structureaccording to claim 2, wherein the electrical resistivity of the centerportion of the electrode section is from 0.1 to 10 Ωcm.
 4. The honeycombstructure according to claim 3, wherein the electrical resistivity ofthe expanded portion of the electrode section is from 0.1 to 100 Ωcm. 5.The honeycomb structure according to claim 4, wherein a thickness of thecenter portion of the electrode section is from 0.2 to 5.0 mm.
 6. Thehoneycomb structure according to claim 5, wherein in the cross sectionwhich is perpendicular to the cell extending direction, the angle whichis 0.5 times as large as the central angle of the center portion of theelectrode section is from 5 to 25°.
 7. The honeycomb structure accordingto claim 2, wherein the electrical resistivity of the expanded portionof the electrode section is from 0.1 to 100 Ωcm.
 8. The honeycombstructure according to claim 2, wherein a thickness of the centerportion of the electrode section is from 0.2 to 5.0 mm.
 9. The honeycombstructure according to claim 2, wherein in the cross section which isperpendicular to the cell extending direction, the angle which is 0.5times as large as the central angle of the center portion of theelectrode section is from 5 to 25°.
 10. The honeycomb structureaccording to claim 1, wherein each of the electrode sections does nothave any boundary portion and is continuously formed in the crosssection which is perpendicular to the cell extending direction.
 11. Thehoneycomb structure according to claim 10, wherein the electricalresistivity of the electrode section is from 0.1 to 100 Ωcm.
 12. Thehoneycomb structure according to claim 11, wherein at a center positionof the center portion of each of the electrode sections in the cellextending direction, there is disposed an electrode terminal protrudingportion to which an electric wiring is fastened.
 13. The honeycombstructure according to claim 1, wherein at a center position of thecenter portion of each of the electrode sections in the cell extendingdirection, there is disposed an electrode terminal protruding portion towhich an electric wiring is fastened.